I have been under the impression that although Finland participated in military action alongside and ostensibly in support of Nazi Germany, they did so out of necessity to resist the USSR and communism. I have also been under the impression that the Finns were generally unaware of the holocaust as they were working with the Nazis, although this thread has told me thats not entirely true.
I have not done much research of my own on this specific topic. I come from a family with Finnish roots, and my grandmother taught me most of what I know about the Finnish involvement. She was not in Europe during the war, but had corresponded often with Finnish family members after the war (I have several relatives who served in a Finnish alpine unit, all of whom claim to have never met a Nazi during the war). She led me to believe that the Finns were in a way caught between a rock and a hard place, needing to defend against the USSR and finding a much needed ally in the Nazis, even though they did not agree with the Nazi regime or politics.
So my question is what exactly is the truth? Do historians view the Finns similarly to other collaborators? Is there evidence that the Finnish military, government, or people were sympathetic to the Nazi cause? If so, to what extent? Is the case from the link above a unique instance in Finnish involvement with Nazi war crimes?
There were certainly people in Finland that were sympathetic to the Nazi cause, and as is very often the case, things were not all that black and white as the simplified versions of history would have us believe.
Finland was a de facto military ally of Germany during the Continuation War, from 1941 to 1944. (The Finnish historical debate has for decades revolved around whether Finland was an ally or co-belligerent, but this is largely a matter of semantics and barely disguised political infighting.) Particularly during the early years of that alliance, when German victory seemed only a matter of time, the political situation gave boost to pro-German and pro-Nazi (which were not always the same thing) elements within the society and the armed forces.
One result of that euphoria were that Finnish government, albeit somewhat half-heartedly, attempted for a while to transform the visions of "Greater Finland" into a reality. In 1941, Finnish forces had retaken the lands lost during the Winter War, and in addition advanced somewhat to what had been Russian Karelia before the wars. These advances had military reasons as well, as they greatly shortened the front lines, but dreams of "liberating Karelia" were a factor as well.
The radicals in Finland, very often at least influenced by Nazi ideals if not outright Nazi sympathizers, viewed the Russians as undesirables and Russian-influenced Eastern Karelians (close relations to Finns, but never before subjects to Finnish state) as needing "civilization." This would've meant, and for a brief period did mean, things like forbidding Orthodox religion in favor of Lutheranism, changing the language towards "standard" Finnish, banning Russian entirely, and so forth.
Probably the most odious result of these policies was that significant numbers of "unreliable" East Karelians and Russians in particular in the occupied areas were uprooted and transported to internment camps. Mortality rates were in some cases very high, and not only because entire Finland suffered from severe food shortages during 1942. While conditions did improve once knowledge about the camps became more widespread within the administration and particularly once it became clear in about 1943 that Germany wasn't going to win, there is no denying that the occupation policy did result to needless deaths of at least hundreds and likely thousands. However, there was no policy of extermination, instead more of a wilful negligence and incompetence at worst - even though individual violations against the laws of war such as shootings of surrendering Russians most certainly happened.
In addition to these crimes, the Finnish secret police Valpo was thoroughly sympathetic to Germans. Its chief Arno Anthoni, a bona fide Nazi operating with the knowledge of the Minister of Interior at the time but in secret from the rest of the government, organized a deportation of Jewish refugees in Finland as well as the attachment of Finnish officers (as interrogators) to German Einsatzkommando Finnland operating in Lapland. During the Continuation War, Lapland was the responsibility of German troops. However, the Northern wilderness defeated the German army and its advance was stymied. This prevented the EK Finnland from carrying out a similar extermination policy as other EKs elsewhere did, but it nevertheless killed probably thousands of Soviet POWs, both communists and Jews. The most recent research is that Finnish officials, particularly Valpo, handed out at least hundreds of POWs the Finns had caught to the Germans in full knowledge of their likely fate; however, this was kept secret during the war and afterwards. Most of the military staff most likely weren't aware of this, but it seems likely they wouldn't have minded much either.
It is still unknown whether and to what extent the Finnish government was really aware of what Valpo and other Nazi sympathizers were doing. Radical right-wing political movements had been essentially defeated in Finland in 1930s, and Finland remained a parliamentary democracy with staunchly anti-Nazi Social Democrats in many key positions. Finnish Jews were not discriminated against (well, not more so than in other democracies at the time), they served in the army just like everyone else, and even had field synagogues - at least in one instance, within earshot of German troops. It is well known that once the refugee deportations became public knowledge (newspapers reported it widely, despite wartime censorship), the Cabinet (except the Minister of Interior of course) was outraged and two key ministers even threatened to resign. This would've likely collapsed the government and precipitated new elections in the middle of the war. This did not happen, but Valpo's deportation plans were immediately stopped, unfortunately not before at least eight (and most probably more, perhaps up to 50) refugees and POWs had been handed over to the Germans. Of the best-documented eight, all but one perished in German concentration camps.
On the other hand, Finland's policy, crimes, mistakes and all, needs to be seen in the context. Recent research also strongly suggests that in 1940, Finland was left with very few good options. Its army had been decimated and supplies of military material from elsewhere than Germany were cut off. It had tried to establish a defensive pact with Sweden, only to be rebuffed by Soviet Union (whose acceptance was a requirement for the Swedes). During 1940, Soviet Union made a series of increasingly threatening moves against Finland, including the annexation of the Baltic states (which had accepted the ultimatum that Finland refused before the Winter War), shootdown over international waters of a Finnish civil airliner, and heavy troop concentrations along the Finnish border, which very nearly triggered a Finnish mobilization during summer 1940. Reportedly, in August 1940 the Soviet foreign minister Molotov asked Hitler for a free hand to deal with Finland in accordance to Molotov-Ribbentrop pact; while Soviet intent cannot be definitely established at least as long as the Kremlin keeps its archives closed, the circumstantial evidence strongly suggests that another invasion was in the works.
Aside from armaments, Finland was also dependent upon Germany on basic food supplies and fertilizers, without which there would have been mass starvation. Furthermore, all alternatives to Germany were cut off after German conquest of Denmark and Norway. So what your grandmother said about Finland being caught against a rock and a hard place has very much truth to it - even though the idea that Finland just happened to find itself as a co-belligerent of the Germans (the so-called "driftwood" theory) is these days thoroughly discredited. Once Finnish government decided to lean on the Germans, Finnish officers participated in the planning of Operation Barbarossa, and Finland's re-entry to the war in late June 1941 (a few days after Barbarossa began) was basically a done deal in about March of that year.
Even then, the general mood in Finland was very suspicious about both the Germans and the Soviets. The latter were certainly hated and feared more, particularly after the Winter War, but Finnish Nazis were a very distinct minority with practically no popular support. (A right-wing Nazi sympathetic "Patriotic People's Front" had more support, though - about the same as the then-proscribed Communist Party.) The government and the military in particular had a strong legacy of pro-German sentiments, but not nearly all of them were any fans of the Nazi regime. The key Social Democratic politicians in several leadership positions, as well as other moderates, were very much against both Nazis and Communists, and they knew full well what their probable fate would be if either extreme took power. (Ironically, it was the leader of the Social Democratic party, Väinö Tanner, who the Soviets stated was the most responsible for dragging Finland to the war.)
So a somewhat accurate conclusion might be that while pro-Nazi sentiments and pro-Nazi individuals (as well as pro-German ones) did exist and influence Finnish society and decision-making, particularly during 1941 and 1942, as a whole the Finnish society or the government was not sympathetic to the Nazi cause. Nevertheless, Finland did fight alongside Nazi Germany.
As for war crimes committed by the Finnish military, in addition to above-mentioned occupation policies and cooperation in handing over POWs (albeit mostly on orders from Valpo), there is clear evidence of sporadic shootings of surrendering Soviet soldiers or prisoners of war (56 individuals were in fact convicted, both during the war and after, although many more escaped unpunished), good reasons to believe in occasional civilian killings by long range patrols (in cases where a civilian stumbled upon a patrol that had to keep its existence secret) and almost-certainty of various instances of mistaken identities, such as a possible destruction of a Soviet military hospital during a long-range raid. Overall, the current research suggests that the Finnish army fought cleaner than most, but perhaps not as cleanly as the British or U.S. armies - although, given what we know from the Pacific for instance, this might be debatable, and in any case crimes made by others do not absolve anyone from any responsibility.
EDIT: minor corrections.