Five year sentence for sexual assault? Sounds like violence was undeniable.
Five years in federal prison for first time drug offense? Obviously over an ounce huh?
How would anyone know whether he's a predator or not, he's been locked up most of his adult life? When he wasn't locked up he was sexually assaulting under aged girls and moving large quantities of illegal drugs.
I know a mothers love is unconditional, but you shouldn't be so concerned with his having to register as a sex offender, you should be concerned with him entering back into society with some sort of skill(s) that will find him a legal means of supporting himself so that he has half a chance to learn what it's like to live a life outside of prison. That's his only hope of avoiding the chance of spending the next decade in a cage,,,,
Help him get into a technical school or entry position in a trade where he can gain experience that will provide him confidence in himself and his ability to earn a legal living. He needs to find some personal value he can offer the world.
After spending every waking moment of the last five to ten years building a bond with criminals, breaking away from them once he's been released is not a very easy thing to accomplish. In the grand scheme of it all, whether or not his name appears on some registry, will make no difference at all!