every time that i've been to the hollywood bowl, they have allowed cameras. however, when i've been to the greek theatre, they allowed cameras with one performance and then did not allow cameras for another performance. they said that the it's all up to the band's manager and their contract. so apparently, it doesn't really have so much to do with the venue, but rather the band itself. but again, every time i've been to the bowl, cameras were good.
if they don't allow cameras, they wont take your camera, they'll ask you to take it back to your car. you can just walk away for a minute and hide it in a pocket though...