Yes. its always better for BA and UX person to work in sync. Because BA mostly focuses on capturing the business requirements & the technology that is used to achieve the same along with other project milestones and constraints. But BA rarely focuses on user level requirements and to understand what is the mental model of the user. So to add that user side to the project its always best that BA and UX person work in sync. If not in sync, UX person should have BA created vision and scope document as a starting point of his exploratory user research.