I've had a venue or two kinda hint like they want a cut of my catering price if they send or recommend a client to me. They did not come right out and say it but I could read between the lines quite well. My thoughts were that it goes both ways, maybe a bride contacts the caterer first and if they don't have a venue I'd recommend a good one that works well with me. I have not had one offer me a cut if I send them work.
Like Bizznessman said, I'm trying to build my business so that the client knows who I am and wants me to cater regardless of the venue or planner.