As you can see from the screenshot, Xavier just announced Daniel Ramsey will have number zero this season. As you might already be aware, Xavier has a dude who wears number zero, specifically rising senior center Tyrique Jones.
I don't know that there is a precedent for this. The rules are usually clear that only one guy on a given roster can wear a number. Xavier is usually pretty good with details, though, so I'm assuming they've cleared this through the NCAA.
The logistical problems are clear: how will officials signal a foul when both players are on the floor?