No addition permissions are required, just the existance of an account (so, you can think of this as elevated over "anonymous," I guess).
Worth noting, and not found anywhere in the documentation is that if you have a forest with multiple domains, you will need an account in EACH domain you wish to synch. This is because the user field does not accept a DOMAIN\Username format, it only accepts the username and assumes the user account is in the same domain you are synching.
Joe