So to update this - The Cisco ASR 12CZ-A doesn't support SNMP on the interface index side. It uses something called "DPIDX" now instead and yes, its Cisco proprietary. So my source port that I want Netflow data from (configured flow monitor M1 input), is being mapped incorrectly by Solarwinds NTA.
When I do the sh command on the ASR to get the DPIDX number of the interface that I want to see as the source in NTA, I see that the Cisco box has assigned a DPIDX number of 7 to my Gi0/0/0 port. That show command is: "sh platform hardware pp active interface all."
Solarwinds is seeing the source port come over as Interface GI0/0/6 (an unused port and no Netflow configured on it) - even though a packet capture on the server is showing that the source port interface is 7.
So, I had to manage that GI0/0/6 port under my ASR 920 node within NPM before I could see any flows. I am getting flows translated in NTA from this box now, the interfaces are just goofy - so its a bit cosmetic, but super annoying that Solarwinds won't own up to their software not translating the DPIDX nubmers from Cisco correctly.
Besides your issues specifically with NTA, how well does Netflow work on the ASR920?