And how often did this happen? If this happened, what was the difference between joining the Russian or the American/British side? Were they treated different? How suspicious were allied soldiers towards Germans joining their side? Thank you for the answers and sorry for my bad grammar.
At the Battle of Castle Itter on May 5th, 1945 (exactly 70 years ago to this day, and 5 days after the death of Hitler), a detachment of soldiers from the Werhmacht fought alongside American troops defending a castle from the 17th Waffen SS Panzergrenadier division, until American reinforcements arrived 6 hours later. This was the only battle in the war where germans fought alongside the allies, and you can read a bit more about it here: http://en.wikipedia.org/wiki/Battle_for_Castle_Itter
Reference: Harding, Stephen (2013). The Last Battle: When U.S. and German Soldiers Joined Forces in the Waning Hours of World War II in Europe.