Wouldn't Diggy have to give the mod to Sylv?
I'm not quite sure how to explain this.
Yes and no, I assume Diggy would have his own user account on Sylv's server, which Diggy can access remotely from his computer. However since it is on Sylv's server, if Sylv really wanted the mod, he could hack into Diggy's user files on the server and take it. This would be another reason why Diggy needs someone he can trust to host.
Edit: Keep in mind, I really have no idea how remote server hosting really works. My explanation is all just based on my intuitive assumption.