It’s not locked in such a way that only Tesla can do it, but it can be hard to find places that will service them. Especially smaller shops just don’t want to go through the hassle of figuring it out, and figuring out how to order parts and such, at least where I live.

Basically, it is going to depend on the shops near you and while Tesla doesn’t seem to actively prevent it I think they make it enough of a hassle for other shops that it may be true in some places that you can only rely on them for repairs.