I wouldn't attempt to guess at how anyone in Hollywood chooses to pronounce their child's name, although I do know that DD and TL refer to the baby as "West" (she's supposed to be named after Mae West).
Tracy, try posing your question on one of the Duchovny fan message boards, like this one:
http://duchovnyforum.com/
Somebody on one of those boards must have heard DD speak the baby's name in a live interview at some time. Then come back here and let us know.
-- Nanaea