Will this run alongside virtual box? (In other words, does it need hyper-V turned on on a windows box?
Yeah, that should work. It usually uses linux namespaces/overlay/unionfs/mount/chroot there are no dependencies on hyper-V.
In the worst case scenario plash would also be happy with not cleaning up mountpoints (PLASH_NO_UNSHARE=1) and using unionfs-fuse. During development I run it on FreeBSD and macOS. So its quite portable. Feel free to send me an mail (mail at irae me) for support.
EDIT: Running it natively on a non Linux-System is probably not what you think, since you can't run a linux root file system for example on top of the macOS kernel. Experimenting with the FreeBSD linux abi emulation layer did not yield usable results for me.