I don't know about the US passport rules - sorry
On the UK side of the pond, a felon is supposed to get an entry clearance before travelling to the UK. No two ways about it. If they show up without one, they need to declare it and come up with a convincing reason why they don't have an entry clearance. If they show up and do not declare it, they risk having it show up in a trawl of the passenger database, and that's *bad* because after that, the airlines are involved and they can be fined for letting him board. So advise him not to go that route.
Because embezzlement falls under the general definition of so-called "crimes of dishonesty", it needs to be declared forever.
On the positive side, family visitors have the right of appeal, both at the consulate AND at the airport. The consulate knows it, the Immigration Service knows it, I know it, the IAS knows it, and there is a general reluctance to refuse family visitors because the Public Advocate for Refusals has *hammered* them for doing it. It's a very strong position to be in.
Also on the positive side, there's a nice loophole that was invented by Jack Straw when he was Home Secretary. He dreamed up the notion (apparently just out of the blue) that a felon should not be refused entry if the IO would be seen as "invidious". It's like, yeah, we all need to be much more sympathetic to the IO's feelings
The actual precedent was set with Iron Mike Tyson...
So to play it by the book, have him submit a VAF1 form to the British consulate. Check the "FAMILY VISITOR" box, and brace yourself for an appeal in the event of refusal.
Tip: I am helping a felon in California get an entry clearance - he did 2 years in a Federal prison
, and I'm gathering character references from faculty members at Oxford, Cambridge, Manchester, and Durham Universities. Stuff like that can help!
If you want to do more research, I use Immigration Law by Phelan & Gillespie. It's great
