The more I work in this field, the more I realize that UX is really a team sport. Especially when it comes to complex product development. There are just too many variables to consider for one person. And I welcome contributions from others; Usually someone's caught a use case I hadn't considered, an error state that wasn't represented or any number of useful insights another pair of eyes helped catch.
Ownership of the UX is shared by everyone who contributes directly and indirectly to the process. That said, yes, the UX person should be the "owner" of the process. But ultimately we all share in the ownership of UX, and that's a good thing.