This may sound dumb but I am asking because I think there is an easy solution to this before I scratch my head too much.
We have a SAN with a filer on top that provides NFS share for other servers.
ServerA and ServerB have this share NFS mounted with no_root_squash. ServerA has userA on it which owns a folderA on NFS NAS. ServerB has UserB on it which needs write access to folderA.
is the solution to create a NFSUsers group on all servers and chgrp the folder to that or is there any other way?
Your solution might work but the best method (IMHO) to handle this kind of problem is to create a central user database, be it with NIS/YP, LDAP/AD or some other method.
You could then create groups for sharing that are automatically synced on all affected servers.