Just to clarify, chameleons aren't deaf, right. I have seen some posts saying that they are, and I don't want to just assume that they are right. ( I play a euphonium and don't want to stress my cham out from the loud noise).
all sound travels as vibrations of air; what we hear is actually the hairs in our ears changing these vibrations to electrical impulses. So to say they "hear" vibrations, is pretty much saying they hear.
From what I understand, they have all the inner workings of the ear but it's covered up by skin. So, ask yourself what you'd be able to hear if you covered your ears....then figure, they can hear that.