haven't heard from support yet, but I figured out what the problem was.. (head smack moment).
I had created a replication policy from DC1 -> DC2. Replication was working, and replicating on the array (nimble).
my problem was, the destination folder in DC2 wasn't configured as a vvol container, just as a nimble folder.
so when i was querying the destination vCenter server, i believe it was trying to retrieve information for the destination vvol container, but that was failing as it wasn't an actual vvol container. it got half the information (including the containerID) from the replication, but then couldn't connect to the container.
remove all replication from that container, created new matching vvol containers on both sides, mounted them both as vvol, re-replicated a few VM's, and what ya know, could see the replication relationship from both sides. and have successfully done a failover. yay.