Both APD and BCSO air units usually broadcast over the area command talkgroups, I've never heard them broadcast over the designated Air channels. If the transmissions sounds like it's being broadcast through a lead pipe, that is the air units.
I too have never heard any traffic on the dedicated talkgroup. As noted, they'll be heard on what ever channel is in use for the situation they're called in to assist with. They're really no different that any other patrol unit, other than the fact that it's a helicopter.