@Scott Brewster - Who owns the LLC that will hold the property? I'm assuming that would be you and the contractor. If that is the case, it is essential you have an Operating Agreement in place that outlines exactly how this will be handled. Well worth the money to a credible attorney.
From what I gather, there are two ways of looking at this:
1) The contractor is flipping the house. You as the lender have absolutely nothing to do with the direct management of the project, you are paid in a fashion similar to what @Greg Bond pointed out above, and you do not own the house. Your interests are protected via mortgage/DoT. This would be a project undertaken solely by the contractor and you are simply a 3rd-party professional serving a specific purpose, nothing further. In which case, yes, earning 50/50 as a lender is exceptional in comparison to what is considered standard.
2) You're flipping the house. It's your money, and you're going to own it outright. Hiring a GC for a job by no means gives them any financial position above and beyond the agreed upon amount they are paid for managing and overseeing the necessary repairs. They manage the rehab, yet you remain top dog and make the lion's share. If you take on this perspective, then your contractor is now the one in an exceptional position to be making 50/50, minus the risk, compared to what is considered standard.
It sounds like your agent and contractor are both new to their professions, or at least that's what I interpreted from "... at the same time I'm kind of kick starting everyone's business too." This sounds incredibly dangerous to me. Not so much as it pertains to the agent, but more so to the contractor. I understand they're your friend, but don't let that cloud your judgment and cause you to make a financially irresponsible/unsound decision. If they bite off more than they can chew, and another contractor has to be brought in, they still get 50% of the profit? Lots of precarious assumptions being made here. Emotion and money should always remain separate, lest you turn an otherwise stellar friendship into a batch of sour grapes. It's all about your level of risk tolerance, and I assume with you being new to this, you want to keep that as low as possible.
Don't get me wrong. I think friends grouping up and tackling new tasks/projects in a mutually beneficial way is incredible and should be strived for. But bear in mind, you're already aiding the inception of their businesses by simply being a repeat client. Your agent gets a front-side and back-side commission from each individual property, and your contractor is brought consistent business (all a startup could ever ask for). At the end of the day, 100% of the risk is yours, not 50/50. This detail can't be shaken off or forgotten. If things go south, you take it on the chin alone, and hopefully have enough funds to take on another project and off-set some of that loss. If your tank happens to be empty, that's all she wrote, which is obviously a risky and perceivably bad business model for any novice (or lifelong pro, for that matter) to follow. I say treat the agent and the contractor simply as they are, 3rd-party professionals. Remain in each other's corner and rip through houses like there's no tomorrow. Then as the trust, understanding, comfort and overall fluidity develop throughout that process, then you can, at your leisure, structure deals as you so see fit.
Hope this helps! Any questions, I'm here.