Yes, absolutely it is supported. Doing so allows you to balance NFS services across the cluster. HOWEVER, there is one rule you must obey and that is that you can only share an NFS mount point from one cluster node at any one time.
So, suppose you had a set of home directories that you wanted to share from /failover/export/home, then rather than sharing that from both cluster nodes (in two resource groups), you would break the shares up into two pieces. For example, /failover/export/home/a_to_m and /failover/export/home/n_to_z. That way, you can share one from one node and the other from the other node using two separate resource groups.
One other rule that Solaris Cluster users need to be aware of: You cannot share an HA-NFS mount point from within the cluster to another cluster node. If you do, you risk deadlocks.
Hope that helps,