It seems that starting with Solaris 06/07 nfs4_domain is required in sysidcfg file, otherwise jumpstart will go interactive. You can force a value, for example nfs4_domain=example.net or you can set it to be dynamic. In that case the value will be derived from the name service in use. Solaris 10 has nfsmapid daemon that maps numeric UID/GID to a string in format email@example.com.
If there is a domain mismatch between NFS4 client and server, the client will see files on the server owned by nobody. On the server syslog might log something like this:
Mar 3 15:13:14 ultra /usr/lib/nfs/nfsmapid: [ID 300081 daemon.error] valid_domain: Invalid inbound domain name example.net..
In my case there was a typo in /etc/resolv.conf file at the end of domain entry. The entry contained trailing dot. This Sun document has all the useful info that might help troubleshooting similar problems with nfsmapid.