I hesitate to post on here for issues I’m experiencing until I’ve
thoroughly troubleshot them, but I’m banging my head against a wall here,
so here I go… 
I initially installed Katello 2.4 on a RHEL7 system,
and as we have a small set of Virtual Datacenter Licenses, I followed the
steps outlined in https://access.redhat.com/solutions/659563 in order to
facilitate the use of them in Katello. I was successfully able to attach
the VDC subscription to ten ESXi hosts, and I could see the derived
subscriptions on the “Red Hat Subscriptions” page underneath the primary
*“Red Hat Enterprise Linux for Virtual Datacenters, Standard” *entry. However,
I quickly found that I was unable to add all the derived subscriptions to a
given Activation Key, as it reported an error that basically indicated the
derived subscriptions shared the same Product ID and would not allow
duplicate additions. This particular phenomenon appears to have been
documented in Bug #13844: Can't attach Red Hat Virtual Datacenter subscriptions to activation key - Katello - Foreman, so I had been
watching it intently, and based on a recent update, this particular issue
has reportedly been fixed in Katello 3.0.
All that being said, I had updated said Katello instance to version 3,
hopeful to take advantage of the bug fix, among other benefits. However, a
few things were immediately obvious to me : 1) After the upgrade, none of
the VDC subscriptions stayed attached to my ESXi hosts. This was easily
remedied by going back through the process of attaching the VDC
subscription to our ESXi hosts, but an odd outcome, nonetheless. However,
after doing so, I found that the derived subscriptions were not appearing
on the “Red Hat Subscriptions” page as they were in Katello 2.4. As I
suspected, that also meant that they are unavailable for me to attach to an
Activation Key. Even more confounding, if I were to hop on a guest of one
of the subscribed ESXi hosts and execute “subscription-manager list
–available”, I could actually see that DERIVED SKU license was available
for me to use if I wanted to manually do so, just not within the context of
Katello.
TL;DR - In Katello 2.4, I was able to attach VDC subscriptions to ESXi
hypervisors, and view the derived subscriptions in both “Red Hat
Subscriptions” and “Activation Keys” > “Subscriptions” > "Add", but
was unable to add multiple derived subscriptions due to the duplicate
Product ID issue reported in Bug #13844: Can't attach Red Hat Virtual Datacenter subscriptions to activation key - Katello - Foreman. This
has reportedly been fixed in Katello 3.0, but unfortunately an upgrade from
2.4 to 3.0 has resulted in a different issue where the derived licenses are
not visible on the “Red Hat Subscriptions Page”, nor the “Activation
Keys” one, but can be seen directly from the “subscription-manager”
command on a subscribed hypervisor guest.
My intent with this is to see if there’s anyone else out there experiencing
the same behavior, as well as possibly getting some advice on a fix from
the experts out there, and/or get some confirmation that this is a
legitimate bug that deserves to be reported (Hopefully with a fix in 3.1 if
so! :-)). Thanks to anyone who may be able to provide some insight and/or
assistance!
Now on to updating said bug report in