Initially I thought it as some interoperability issue, but that wasn’t the case. I went ahead and looked at the dashboard, and it reported that the Adapter Instance Object is down, as follows:
I clicked on the alert link, which took me to a more detailed description of the problem.
And there we have the root cause of the issue – my license (vROps Standard) does not support the NSX-T Adapter. Apparently this adapter is only supported with vROps Advanced or Enterprise Editions. Once I upgraded my license edition, the collection started correctly once I stopped and restarted the NSX-T adapter. Very soon, I had the NSX-T Main dashboard populated with my NSX-T environment information.
As I hadn’t come across this behaviour before and couldn’t find it reported anywhere, I though it would be useful to share in case anyone else stumbled across it.