Since this article, Cloud-Init supports FreeBSD, NetBSD and OpenBSD natively. Cloud-Init handles all the interaction with the Cloud provider and the metadata. So beside constraint of the disk image format (qcow2, raw, etc), the same Cloud-Init base image is likely to work for different Cloud vendor seamlessly.

I maintain some Cloud images (qcow2) for BSD https://bsd-cloud-image.org/ that are based on Cloud-Init.