Just label them as such. However, if you have 1 or 2 great character voices, don't bother with a separate tape. HOW they're integrated so you don't confuse the listener. If you put more than a few character voices on a straight read tape it gets annoying. So, if you have more than 2 or three characters, you definitely need a second tape.
LA has an enormously viable character voice market via the cartoon shows.
They're not produced in New York or Chicago or Miami or Atlanta or Des Moines. The answer may be yes, but the reality may be no. A DJ who could do blowaway character voices was booked on a straight spot, and it was a disaster. It was assumed that if his ear was good enough to do all those voices, he would have a good enough ear to at least take direction and give line readings. The guy couldn't hear anything.