"Are these the type you don't want to rest the hammer down on a loaded chamber because they could go off if dropped?"
No. They're perfectly safe.
"He also claims the stainless to be one of only 18 in the US. The remainder of the 2500 lot manufactured having been shipped overseas."
Possible, but very unlikely. 629s are the stainless models. .44s aren't a big export item, though, not like the .357s and .38s.
Serial numbers and pictures of the supposedly rare stainless one are necessary.
Also, open the crane on the stainless one and see if it's marked 29 or 629. If it's marked 29, it's likely nickle plated, not stainless.