What was your arrangement with the group?

Again, with a PML your arrangement can be whatever the two of you agree to so yes, it's plausible they could defer payments until the unit is rehabbed and refi'd or occupied.

My problem/question is that after getting my RE license I need sponsorship from a RE broker, at least for the first 3 years.  

In my experience if you are below what the FHA requires for a loan (580 i think is the minimum) there is usually a way to get your credit score above that threshold in a time frame similar to similar to finding a home that is in your cash budget and then getting a loan, most likely at a very high interest rate if your credit score is still low, to fix it up.If you have a little cash on hand, and you have a 3 or more collections on your credit report, you can easily bump your score by 25-50 points by offering the collection agencies pay for delete arrangements.

There is an exemption in the Code that allows for reasonable compensation for management  found here IRS Code §4975(d) and/or Department of Labor PTE 96-62.   2)any contract, or reasonable arrangement, made with a disqualified person for office space, or legal, accounting, or other services necessary for the establishment or operation of the plan, if no more than reasonablecompensation is paid therefor;The key is operaration and reasonable fee. 

Do you have any lessons learned over the past year that you could share about this arrangement?

I know that there's a way to arrange it such that in the event of a default, ownership of the mortgaged property would immediately return to me (again without having to go through the foreclosure process).

So, like I said...go find some deals first...THEN you can worry about how to arrange the closing.

Have a conversation about expectations and if the arrangement isn't working for either of you, go get a different agent.

Many landlord associations have arrangements for their members to get reduced price checks (approx. $15 inc. tax).