Belt drive to chain? Help.

For example, if I pedal the bike with the wheels off the ground backwards....it actually spins the wheel. I don't think this will be good for the bottom bracket long term.

Don't get what you mean by this? You lift the back end of the bike off the ground, turn the cranks backwards and the freewheel equipped rear wheel rotates backwards with the cranks? Would that be affected by chain/belt tension?