The 30 Year War did not contain any army that the label "humanitarian" can be applied to even in a relative sense IMO. Consider that even at the time English writers of the civil war blamed the harshness of the conflict on the officer class who had served abroad and bringing the "German way" to England. I'm not sure that's quite right (civil wars tend towards brutality anyway), but a great number of officer served in the 30YW first and I think it is safe to say a majority passed through the "Swedish" army.

Now the army itself I qualify as "Swedish" just to point out that the vast majority of it's strength was not actually from within the bounds of the Swedish state. And a large part of the domestic troops ended up in garrison service to protect communications back home. Wisely as it occurred from time to time that underpaid mercenary garrisons simply sold the city they guarded to whoever paid the best.

The largest contingents (I'll caveat that numbers and fractions varied wildly over the years) were German mercenaries at the entry of the war the Swedes took over the battered but experienced northern protestant army that had fought for the Danes who had sued for peace. The second largest cohesive group were the British, Englishmen, but in particular Scots, the British were consider very reliable as unlike the Germans they had no political ambitions or local agendas.

The most significant source of financing was actually French subsidies paid to Sweden as part of the alliance. And if the French were late with reimbursements problems arose. Gustav II Adolf did himself say that war should sustain war, but that was the thinking and actions of all armies in the 30 YW. There existed no reliable logistics or concept of such yet. Armies lived off the land because they could and they must. If you were luck and an ally you might get paid for the goods. Towards the later stages of conflict being forced to support troops in a town was about the worst that could happen, whether they were ostensibly on your side or not. Conduct usually depended on local officers and their ability or willingness to control troops.

Now Gustav II Adolf did adopt fairly strict articles of war for his troops at least officially reigning in pillaging and such, but wasn't out of the goodness of his heart,at least not wholly so. There was no room for "private initiative" in this regard. If the "Swedish" army in the initial year(s) didn't pillage as much is was because they were moving through supposed friendly lands they were liberating (Protestant Northern Germany) or allies which had already been ravaged years before. Sometimes you intentionally destroy areas for revenge or strategical reasons. So e.g. the lands of the Bavarians, leaders of the Catholic league and a lynchpin in the Catholic effort was especially targeted to give them taste of what they had inflicted upon the north and reduce the capacity to wage further war. As the years wore on and Gustav II Adolf was killed the war lost focus and armies had looser reigns to acts as they willed. Even more difficulties of paying and supplying troops encouraged troops increasingly to take to it themselves.

In short, no I have never heard any military man advocate for "humanitarian war" from the Swedish armies of the 1600s or 1700s. Strictly speaking of course it is entirely possible, but none of the conduct of Swedish arms really bears it out. The closest we get might be the later armies of the 1700s where, again, military discipline was stricter and there was a harsh regimen for conducting operations. But again it wasn't entirely a question of being nice, but because there are military strategic considerations to it. The later armies were also more tightly national and supported differently and not as expected to feed of the land. Not that stopped armies when they could of course. No army except possibly the Americans in WW2 were so well supplied they could ignore good opportunities if they presented themselves.

I really don't know where you got that from, and I'd be really sceptical of its source. The 30 Years' War was one of the most brutal wars in European history, and the Swedes under Gustavus Adolphus were just as, if not more, guilty of that as their enemies.

From Chrisopher Clarke's The Iron Kingdom (ISBN 9789085426356), which focuses on Brandenburg-Prussia, a picture emerges of an apocalyptic level of destruction for this battlefield region. Towns were destroyed, cities plundered and extorted, houses torched, women raped.

There was also widespread torture. Reports on the conduct of the Swedish army in particular include mention of the so-called 'Swedish drink' used in Beelitz (near Potsdam). Here a piece of wood was inserted into the throat of an extortion victim, moved around, and used to shove in water, sand and feces. They also include Swedish soldiers roasting people alive in Lenzen. The image that emerges from Clarke's chapters on the 30 Years' War is certainly not that of a law-abiding Swedish army and a plundering Danish/imperial army; all armies behaved equally barbaric.

For Brandenburg in particular, by 1648 the 'Great War' had cost the lives of half (!) the population of the Electorate, with regions such as Löcknitz having mortalities as high as 85%. The war is sometimes blamed for the lack of indigenous folklore in Brandenburg: so many people died that there was a breach in continuity between the pre-war and post-war generation. There were simply not enough people left to effectively pass down customs.

And Gustavus Adolphus personally can be blamed for pulling Brandenburg into the war. He threatened and cajoled the Prince-Elector Georg Wilhelm, who tried everything to remain neutral, into an alliance, saying:

I do not want anything to do with neutrality. [The Prince-Elector] has to choose between friendship or hostility. Once I reach his borders, I expect a choice. This is a fight between God and the devil. If my cousin wishes to choose God, he should choose my side; if he wishes to choose the devil's side, he must fight me; there is no third option.

(I apologize if the above quote has translation issues: I'm using a Dutch translation of an English translation of the original German.)

So in conclusion, I don't think Gustavus Adolphus can reasonably be called a humanitarian.