Several of CAS' poems in translation are attributed to Christophe des Laurières. "Mors" is one such example:

[www.eldritchdark.com]

It's my assumption that "Christophe des Laurières" is actually a pseudonym for CAS himself, since des Laurières appears to be unknown outside of his connection to CAS.

Does anyone know for sure if Clark Ashton Smith and Christophe des Laurières were in fact the same person?

Ah, I should have done a little more research before posting this question - looks like Donald Sidney-Fryer identified "Christophe des Laurières" as one of CAS' pseudonyms in the relevant section (page 261) of Emperor of Dreams: A Clark Ashton Bibliography. The answer was right there on the bookshelf, I just had to seek it out!