You shouldn't have any problems with having your receiver in a closet. Just leave the sides and top open to allow for air flow.
We've had our DirecTV DVR in a home theater credenza for almost 4 years. With all the other 'stuff' in there generating heat, it gets warm enough to seemingly cook eggs! But no equipment issues. I've got enough holes in the back of the cabinet (and the doors on the front aren't sealed) so we get a reasonable amount of air flow through things, it seems.
Bill
