There is one Betelgeusian seen full-length in the TMP rec-room briefing scene -- he's the third guy from the right on the balcony, in a brown uniform.
He's clearly humanoid in shape, with no wings.
There's also a pretty good shot of the Betelgeusian science officer (whom I named Hrrii'ush Uuvu'it in my novels) here at Memory Alpha
Vilix'pran was pretty much meant to be nonhumanoid, which suggests not just a human shape with wings stuck on, but something more radically different in body shape. That was the point of the running gag: since he was never seen, he could be as bizarrely nonhumanoid as the writers' imaginations could make him.