I don't think you will have any issues in YOU take regular backups and YOU retain the credentials to your registrar.
I own UnixGuru, but I don't work there full-time, so I have many colleagues who host with me.
It's a tricky one, just ensure that you work with your colleague as you work with any other host. Don't take liberties with one another. You pay on time, and they provide good service.
If they require a compromise, then maybe you should look elsewhere.
I'm assuming this guy does this "on the side", in which case, if your site goes down during the day will he be looking at it?
I work elsewhere as a consultant, but I have full-time employees looking after my systems.