The only argument that I have is that the constraints in the validator jar can be used by any implementation.
Size is not an issue since validator is pretty small.
I'm not sure if the provider is automatically registered in the server but optionally that could be an argument too.
I don't think the annotations defined in javax.validation would need to be included.
I would think that if there is support for the validation api all should be present.
Also for a standalone application you would then have to include the full hibernate validator anyway which would contain those so I think no need.