I haven't heard anything about them being different species, living in AZ they are always referred to as C. exilicauda. I know with most websites I have seen they either list one or the other, and the one that lists the C. exilicauda are usually newer sites, I haven't seen any where the two names are both listed. I'm part of the Arizona Herpetolgocal Association and sometimes on the forum people post asking about barks and calling them C. sculpturatus and people usually correct saying that is the former name.

I wish I could have a more definite answer for you! Thats just what I always thought was going on with the names.