How have you been? Nice to see you around.

You can certainly run a hot tub using BBB. You'd want to drain the tub and start fresh (see the 'Once a bromine pool, Always a bromine pool' article in Pool Solutions).

Is the spa indoors or outdoors? It makes a difference as to how much cya you'll want in the water which, in turn, will determine the chlorine level you'll want to maintain.