Well, really, if it's a singing role in a musical, then it is also an acting role.
I think I know what you mean, though. It's been a while since I've seen it, but I'm pretty sure it's an "acting" role. I think that was who a friend of mine played, and he is DEFINITELY not a singer (and only sang the chorus stuff in the show). And, please, someone correct me if I'm wrong!