There are some sleeper trains still in Germany - although you need to pay a supplement on top of the annual train-ticket to use them. It would limit you quite heavily to certain transport coridors though.
As mentioned elsewhere: none of these are free with the BahnCard 100, and most are fully booked quite a while in advance. He sleeps in regular night trains on the floor or on some seats, not in bunk or bed on sleeper trains.
