Actually, yes. You can place a wager and have them set the lines at 20 1/2 wins. You'll certainly get much better odds. I say go for it. At first glance I would say under most definitely. But the last time I thought the Rockets was going to suck badly, they ended up with 42 wins. So I'm not going to bother guessing.
I would take the under. Rockets always suffer injuries to key players and lose 2-5 games because of it.