I don't have much experience working with NIS at all, as I came from an LDAP environment. I have a project to move a bunch of clients within a NIS domain to point at a new NIS master server. There's no config management in place, and no real authoritative list of every machine in the domain.
How do I verify that no NIS clients are talking to the old master? I don't see any ypserv log files (the old master is a RedHat AS 3 box...), and AFAIK there's no reliable way to tcpdump for NIS traffic since it uses RPC.