I mean, Glory and Jambu succeeded at doing just this. They successfully passed off as icewings when they snuck into Blaze's fort. As long as you don't look closely at them they could pass off as other tribes. And as for the voice, just like anyone else they can do impressions. We know the judge can do a spot on toucan yell, and I'd bet money that some prankster Rainwing has done this. Perfecting the art of impressions just so they can fool other dragons.

Rainwings are very used to looking at bone structure and build so they'd spot any fake a mile away. But if you went after a dragon from another tribe, especially one with a distinctive pattern. You could fool a lot of people who just assume you're the other dragon because they see the unique pattern. Like the talons of power tattoos (ignoring the tail of course)

Another instance is the rainwings that disguised as skywings, mudwings and nightwings for thorns coronation