I know it's done. I've just never had to think about it before. On the one hand, it sounds unethical for him to lead us into a contract, then leave and come work for us. On the other, our product is awesome and will solve a key business problem for them. It's a no-brainer for him to midwife a deal between us and his company.
I feel kind of weird even bringing it up to him. Maybe I just need to sack up.