Safe to use Wheel Adapters 5 on 4" to 4.5"?

Sounds like horse **** to me. Spacers are far worse than a billet adapter. Most people just put a spacer on without even increasing the the length of the studs. Quality adapters wouldn't have that problem.
I would call a small mom and pop tire shop. Large corporate stores won't do a lot of things for liability reasons, but they are wrong about the spacers in my opinion.