Guards were in some cases forced to take part; however these were not German SS guards. For example, Ukrainian recruits to the SS and Jews forced to take part in the slaughter and maintaining of death and concentration camps were common.

The movie Schindler's List demonstrates how Jews were recruited to help police the Ghettos in Poland, and they were then involved in the liquidation of the ghettos and transport to camps. They also played a role upon arrival at the camps.

At the camp of Treblinka II (the extermination camp in the Treblinka complex), disguised as a railway station, 800,000 Jews and Gypsies were murdered by a team of around 25 SS men and about 100 Ukrainian auxiliary Wachmänner in just over a year. Aside from the astounding figures, this demonstrates the use of foreign employees (for lack of a better word) in the system used to achieve the final solution. Sadly my source does not state whether the Ukrainians were forced to work at the camp.

I would like to also quote Konrad Morgan, an SS soldier who sheds some light on how he was recruited into the SS.

'After the change in 1933 [election of Hitler as chancellor] the SA and SS leaders appeared on the sports field and then we got a new sports instructor and then we heard that this instructor was a former offer in civilian clothes. Then these sports and exercises got more and more like pre-military physical practice, and then we had formation exercises as well. And they said, by the bye, it would be quite nice if you could wear a brown shirt, then a brown tie and then boots and so on. And so gradually a uniform grew up, a big makeshift, but it already looked somewhat military and then we often had to march routes and parade ourselves and then one day there was an inspection. After the inspection they said, on the basis of height, that lot over to the right and those over to the left, and the we heard, in the future those will belong to the SS and those to the SA. And so I came to the SS.'

I think it provides an interesting insight into how ordinary Germans were swept up in the tide of the changes and new policies of Hitler during his rise to power and the aftermath.

I apologise for this being a slight jumble of quotes, facts and references, but I tried to pick some related information that might provide context to this question and any other answers through some information on guards in the camps and how those SS guards may have come to be in the SS.

Sources:

The Second World War - Antony Beevor

The World at War - Richard Holmes [Transcripts of all the interviews filmed for the TV series The World at War]