Teeth have no place near a penis, ever.
Sucking is great though, as long as you aren't sucking TOO hard. Maybe he could tell you how rough he likes you to be with it and then it's win win. He gets the best oral of his life and you get the confidence of knowing you are the one who gave it :)
Oh, a little bit of biting can also cause blood vessels to break, too.
It could be anything from a broken blood vessel (which is pretty much a hickey) or an STD. Any type of trauma to the penis can cause blood vessels to break. Is it tender to the touch? Does it feel warm? If so, it's probably a blood vessel broken. It could have been caused by a number of things, your fingernail digging into his penis, him pushing too hard...ect...I wouldn't worry.
But yes, a hickey can show up anywhere where there are blood vessels...pretty much your entire body.