Dennis is correct about the ID requirement. The problems arise when someone else uses the input frequency not knowing it is being retransmitted on another band. So the question is, are you responsible, and the answer is yes! Have any amateurs been cited by the FCC for improper IDs while using cross band repeat? The answer is yes!
Crossband repeat seems to be the rage for whatever reason. Perhaps it is viewed as a poor man's repeater, which it isn't. It is legal, but you have to follow the rules, and there isn't much leeway.