One nice thing DO and Vultr has is built-in support for FreeBSD (both) and Windows Server (Vultr). That said, I run OpenBSD, FreeBSD and SmartOS VMs on Linode through a manual install process. The only issue there is password resets through the web UI don't work and backups wouldn't work either.

Here is the guide I used to get FreeBSD working [0], and the others were easy to figure out from there.

[0] https://www.linode.com/docs/tools-reference/custom-kernels-d...