Sorry, only found this post today. In case it remains an issue for you or to support others in the same situation....
I ran into the same situation. in my case, my intent was to host both instances of vIN in the management cluster. one would support collections from vCenter-M and one from vCenter-R. I recall when we deployed the 2nd instance, the license key selection screen briefly presented the vCOPS suite key then it disappeared. Without it, registering is impossible.
It turns out that the OVA deployment process in this case requires you to deploy vIN to a resource cluster managed by vCenter-R. When I took this approach, the vCOPS suite license based on vCenter-M but exposed to vCenter-R via Linked Mode was sufficient. That is, there is no limitation concerning the number of vIN instances.
I considered deploying to vCenter-R to get the appliance working then re-registering it under vCenter-M but deemed the work involved not to be worth the time and effort.
IMHO, supportability aspects of vIN are poorly implemented.