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? How will the PA guy make announcements? How will opponents scout by jersey number?
Those are all hurdles Xavier will have to clear. I'm sure they'll figure it out, though. After all, I can't think of any other explanation for this tweet. Can you?