We do this with one of our products (nextproof.com). We process print orders on behalf of photographers, take a %, then disburse funds to photographers on a weekly basis if their balance is > $100. Most transfers are done via ACH but we do mail checks to a small number of people.

We use BrainTree for all this and they were very helpful. The technical terms they used for this was "third party payments aggregation". Because this is riskier for them, our account had to be underwritten by a different company than they normally use. Also, a portion of our funds are held in reserve for an additional 30-90 days (I can't recall).

Anyway, if what I described is what you want to do, yes its possible and legal. Just make sure you cover all your bases with good terms/policies. Tell BrainTree what you want to do and I'm sure they will help you out.