This is how I was able to use the Windows 10 upgrade on both boot camp and the VM using boot camp. fwiw, I am starting with an upgrade version of Windows 7 Pro that I had already installed and activated on both boot camp and the VM boot camp (I used the reset "slmgr /rearm" method to allow the activation on both machines.)
1. I upgraded my Win 7 Pro Boot Camp partition using the Windows 10 upgrade and activated it.
2. I erased my current VMWare Fusion Boot Camp machine, then added the new Windows 10 boot camp as a new machine.
3. I went to VMWare Tools and added a new virtual disk.
4. I installed my copy of Windows 7 Pro to the new virtual disk and booted from it.
5. I used the downloaded version of Windows 10 media creation tool and installed from that, making sure to not add a Product Key (see http://answers.microsoft.com/en-us/windows/forum/windows_10-windows_install/windows-10-upgrade-problem/d5cb3c55-9efb-4691-8669-8aaab9a7586d for more info)
6. I went back and opened up the Windows activation and it activated as genuine (booted off of the new virtual disk.)
7. I then deleted the virtual disk thereby booting the VMWare Fusion machine off of the boot camp partition.
8. Voila! The boot camp partition was activated in the Fusion machine.
9. I rebooted my MacBook from boot camp and confirmed that the activation was still good there.
Now I have a couple of issues,
1. It appears as though my Office 2016 install still sees the 2 installations as separate installations. I have an Office subscription with 2 installs so that isn't too much of an issue, especially since I also have a standalone Office 2016 install for my Mac (thanks to the Microsoft Home Use Program.)
2. When I boot up in boot camp, I am presented with a boot error screen. It appears as though the Windows 10 boot still sees both the real install and the install I made to the virtual disk. It was defaulted to the virtual disk so I was having to go back to the boot screen and choose the other Windows install (on Partition 4) to boot into my real partition. I finally figured out how to get to the screen to default to the boot camp partition, but I still see the boot option screen when I first start up the MacBook in boot camp and then it goes away and boot from the proper partition.
At this point, I am trying to figure out how to eliminate the extra Windows boot partition so it will go directly into the boot camp partition but after trying to figure out how the EFI and Mac Boot Camp deals with partitions, I still can't figure it out. At least it is just an annoyance rather than something that prevents the boot.