So I was trying to answer my own question, here's what happened....

Apply a GPU to a NH flight (D fare) - was expecting an error message or that upgrade space is not available. To my surprise, I got "Upgrade Space Available"!!! I thought "too good to be true", but I clicked "apply" anyway and here's what I got:


Conflicting message huh? I clicked "Cancel" and thought that was it, however, I noticed that 1 GPU was deducted so I went on to ANA's site and checked my reservation and here's what I saw:



Normally to get that "Upgrade Waitlisted" on NH, I have to request it on NH's website, and use ANA miles for the upgrade.
The change is also reflected on UA side as well.

Interesting, huh?

Does this mean that the problem of not being able to wait-list upgrades on LH flights is on LH side and not United?