Can a T8 bulb work with a T5 ballast?
It won't work right.  It will overdrive the tube (or underdrive the tube) and you'd get short tube life.  It may flicker horribly.  It may not be able to strike.   

Basically the same things that will happen if you put T12 tubes in a T8-ballasted fixture.  

It's basically a dumb thing to do.

If you got a wrong thing, take it back and get the right thing.  

This may not help, but.. You know, if you have a T8 fixture and it uses anything like standard tombstones (lamp sockets), they sell special extension tombstones to fit a T5 bulb.  Or if the fixture already has that upgrade, you can roll it back using standard tombstones.  

Though the T5 is slightly more efficient, all things being equal.