You should, of course, speak with your own plastic surgeon about this.
My answer would depend to a certain degree on how large the seroma is, how it's being treated and whether it's resolving, staying the same, or getting worse. In the first case it should be okay to engage in gentle physical activities (of any type) carefully but if the condition is worsening I would advise against that. And in that case you should consider a different form of treatment. Many if not most seromas resolve spontaneously but if it's relatively large or not subsiding with the current treatment it may be a good idea to have it drained. This, too, is something you will need to discuss with your plastic surgeon.
I hope that this helps, and good luck,
Dr. E