It's usually the elaborate, "cloudy" stuff that prevents booting custom OSes (mostly just networked storage, e.g. https://github.com/scaleway/image-proposals/issues/11 Scaleway would need a Network Block Device driver to run FreeBSD).
Normal "VPS" providers often support this, e.g. prgmr just lets you boot into a recovery image (Linux, FreeBSD, NetBSD) and do whatever you want to the virtual hard drive, install anything that runs on Xen there. It's like running a Xen VM on your own computer, except it's someone else's computer.
Interestingly, Digital Ocean uses local storage. I guess the issue was just with the boot process.
Normal "VPS" providers often support this, e.g. prgmr just lets you boot into a recovery image (Linux, FreeBSD, NetBSD) and do whatever you want to the virtual hard drive, install anything that runs on Xen there. It's like running a Xen VM on your own computer, except it's someone else's computer.
Interestingly, Digital Ocean uses local storage. I guess the issue was just with the boot process.