@buldamoosh Oh yeah, you can't disable CBT on a snapshot. It is inherited from the VDI it is the snapshot of.
You can vdi-destroy the snapshot instead of forgetting them 🙂
But yeah, it is "normal" that the snapshot are not removed by the migration.

CBT will be enabled by XO if you have the NBD+CBT enabled on your backup job.

Indeed, as per @Danp

Xen Orchestra provides an OVA importer. Since VMware decided to play dumb and not supporting OVA exports, you have 2 options:

create an OVA yourself, it's trivial: it's a tarball with the OVF and VMDK disks. XO is capable on reading the OVA, prepare the VM metadata and then will import the VMDK import the VMDK in XO directly, and create the VM metadata yourself (I think we could easily add OVF metadata read import in XO since we already do it with OVA)

I really do not understand why (well I think I did) Vmware removed the OVA export feature despite it's a lot easier to deal with.