Yes, it boots fine as Filedisk from internal HD and also from USB device, and my old 7x64 VHD also did, but I don't keep the 7 VHD anymore.
Maybe you should try making the first 7 installation (using a VHD native bootable version) on a VHD located on a USB device, as long as the VHD and the Boot files/folders will be on a USB device, then WinNTSetup will take care to make all required modifications to load the USB drivers on appropiate timing, (this is based on cdob old commands [valid for USB 2.0 and USB 3.0 if available] made long time ago), You will see on WinNTSetup the option for Enable Native USB Boot on Windows 7 on the very last window just before starting to install, see attached picture, but this will be present only if installing on a USB device, if doing the installation this way USB boot watcher is not necessary.
My WimbootCompress.ini is the same we have being using, attached if you want to confirm.
My 8.1 x64 VHD (and the old 7 VHD I deleted) also has installed diskmod filter driver so it is able to see all USB removable drives as fixed disks, then it is capable to see all flash drives partitions, just as 10 does now. Attached for your convenience (including also a version signed by Paraglider long time ago).
alacran
WimBootCompress.zip
diskmod.zip