I did this upgrade/migration this weekend.
After the migration to VCSA, I started upgrading some host. It is important that you to a rescan of VC/hosts after the upgrade, as I got backup failures before I did that. After a rescan, everything worked as before.
The first run was not an active full, but it seems that CBT was reset automatically, as first run seemed to read all data from the VMDKs (but only transferred the changes)