Tonics should definitely be compatible, given the positive response to BXBZTMT, which you can continue for a while until the dog strengthens further.
My first temptation would be to add a Kidney tonic, and I would wonder first about Ba Wei Di Huang Wan (Rehmannia 8), given the role of Dampness in his pathology (as shown by response to treatment).
Another idea, though, is to try Yi Yi Ren Tang. Classically, it fits a bouyant floating pulse, but could also fit the purplish tongue and weak pulse. This is because it is a Damp drainer, Wind expeller, Tonic, and Blood mover all in one, so a broad array of pulses will fit it. I would maybe give it a go first, but see what your intuition tells you. It's apparently quite accurate these days!