Thanks, cfor.
I'll double-check the other suggestions (though I've done enough rounds with DNS that I'm pretty sure it's settled), but the transfer space is definitely an issue. Time may also be a factor, as they are in different clusters.
We have two cells in a DMZ for customer access and a third in a trusted Management VLAN/segment behind a firewall. The NFS/transfer server sits out in the DMZ with the other cells. When I'm watching the cell.log at the start/restart of the vmware-vcd service, I see a notification about something to the effect that "the management cell's use of the NFS transfer space cannot be verified." Maybe this is a bigger issue than I had realized.
Time to check the firewall ports again, I suppose...Is there a quick way to manually verify that the mount operation is happening on that management cell? (It's configured in init.d, but I'm not a master of NFS on RHEL enough to troubleshoot it.)