well, I'm a bit confused what your exact issue is, but here is how I mount on my Redhat server an AIX mount:
10.28.1.61:/u37/somedir /mnt/somedir nfs rsize=8192,wsize=8192,intr,posix 0 0
and on AIX, that export looks like:
portal2 being the Redhat box. Key is making SURE hostname is in /etc/hosts on the AIX box and that your UID/GID matches up between the two boxes. I hope this makes sense.