Should I become a partner or a subcontractor in a new business venture?
You could also work out a deal where you would pay commissions back to the established business based on the numbers of leads and customers the established division routes to your division. Essentially, all of this is open to negotiation, and the first rule of negotiation is that there are no rules. It is simply finding a solution that will work best for both of you--so you can both share in the success of the new venture.
All the best.