Yes, no, yes, maybe
Dermaplaning over active acne
is not a good idea; it increases the risk of infection & scarring
Hair grows back normally, since dermaplaning is basically a very close shave. Blackheads are plugged oil glands, and the most basic lesion of acne, but blackheads by themselves are not acne per se. Dermaplaning will probably not make blackheads worse, but it is not a treatment for blackheads either.