Actually, KG200 was probably the one you are thinking of. I think I posted my article about captured eagles a while back here. It was about American aircraft captured and flown by the Luftwaffe. I could have done another full article on the British airplanes captured. One of the books that is fairly accurate ( I may be a bit generous) is "Strangers in a Strange Land, Vol. I" by Han Heiri Stapfer. There are some great pictures of the captured craft in there, although some of the stories of how they were lost by the allies and captured do not jibe with the veteran accounts and official unit histories.
Some of the bigger aircraft were used in clandestine missions and bomber scouting. Many of the fighters were tested extensively by the Luftwaffe before being turned over to Zirkus Rosarius, hich was a group that used them to train Luftwaffe pilots how to fight them. They also flew them in mock engagements to better train the pilots. Believe it or not, that was the basis for "Top Gun" and "Red Flag".