It seems that tcpwrappers does not honor netgroups. As this was noted in a different unrelated bug, I'm opening this one: https://bugzilla.redhat.com/showbug.cgi?id=440114#c8
It seems that netgroups are not working; if I put in my hosts.allow file
mountd: hostname - or - mountd: ip-address
then I can mount, but if I have a netgroup, I can't... for instance
mountd: @selectedhosts
Can you confirm this behaviour?