What Role to assign remote site developer?

“Developer” implies that he will have access to the code – in which case he has carte blanche to do whatever he likes.

If you actually mean he just has access to the site admin – and I assume this is multisite as you mentioned being a Super Admin – then a site Admin cannot remove a Super Admin / Network Admin.

Capabilities are very atomic – meaning if you wished to you could create a custom role with just the caps you want him to have access to.