Ok, so the VT bass can drive a power amp, but....

[Nyarlathotep]

... Would you be able to stick a TU-2 (or something similar that's not passive like a simple ABY) after it to split the signal to two power amps?

I imagine this pretty much applies to any preamp + buffer split combo....

[dannybuoy]

The signal would probably be too hot and you might get clipping from overloading the Boss - if so you could probably split it passively without too much trouble.

[smo]

It may work at cranked volumes, but I wouldn't try it unless you can afford a new tuner. and/or you do it very carefully and listen for any sign of clipping etc.
But as long as the VT is set at guitar/instrument unity gain volumes you should be fine tho.