Hulk can survive a while in a vacuum. The latest example is a recent issue of Avengers were Starbrand blasted the Hulk into orbit. Carol Danvers went to retrieve him and used him as a missile. It was all kinds of awesome.
Whether Supes can do the same seems to fluctuate. Back in the day he seemed fine flying between stars and galaxies but in the modern era he's often drawn with a breathing mask in space. I'd say he can survive a while without breathing but not indefinitely.
it might be poor form, but Superman could chuck Hulk into space, and just leave him.
Saying that if Superman does need some breathing kit, he can chuck hulk, get the breathing equipment real quick, and then follow Hulk.
Then again is there anywhere in orbit Superman could chuck him, and not stand a decent chance of hitting something?