Update Windows 10 Enterprise PC to 1511 per DVD

Yes.

I had exactly the same issue, and eventually (Dec 1st) gave up waiting.

Mounted the ISO, ran the setup, and ensured that Keep Files and Settings was selected when given the option.

As soon as the install completed and I'd rebooted, Windows Update straightaway started offering me updates again, including the Windows Defender ones which I'd been getting every day anyway, but more to the point, the cumulative updates were also coming through.

My Win 10 install was clean on to bare metal on 29th September (so a lot more than 30 days ago), I didn't have Defer Updates selected, and I hadn't installed the update and then uninstalled it again (in fact, I don't think that's possible with 1511).

But yes, update-installing from the MSDN 1511 ISO seems to work fine, and unblocks the flow of normal Windows updates.