It’s possible, depending on how they set up their definitions. If they see time as an axis that precedes creation, then even if there isn’t anything that exists in space, then there is something that exists along the temporal axis that would, technically speaking, preclude the notion of ex nihilo.
(That being said, if you carefully define what creation ex nihilo means, in the b-theory framework (such that you’re talking about ‘nothing’ physically, per se), you could still hold to the concept. Moreover, if that definition places God outside of the time axis (and gives rise to it), then creation ex nihilo still works.)