You will almost certainly encounter chainstay interference with both the crank arms and the inner chain ring if you try using an external bearing type BB which cannot be adjusted for width.
If you use an older style square taper or Octalink, you have a chance by using a longer spindle.
You need a wider chainline anyway on an MTB than you will achieve with an external type road crankset.
The next issue you will face is getting a road derailleur to adjust out to work with a 50mm chainline. Some might do it, and some might not.