The Thing was immune to the Legacy virus, the organo-metal virus, and all regular viral shit, so I don't think The Thing (1982) could assimilate him. His DNA, if it exists at all, would be pretty much impossible to access. However he has been known to 'shed' sand-like detritus, so that may be enough for 1982 to mimic him.
The Thing from another world would be to disgusting to assimilate the thing, not because of the rocks but because he's Jewish. Richard Masur was jewish but he got shot in the head so my joke still works