Thank you for replying.
I've got synoboot, synoboot1 and synoboot2 in /dev.
Grub.cfg is untouched except the s/n and mac, and the VM is pretty standard as per tutorial, except the sata controller passthrough.
I migrated a bare metal install to esxi, it was pretty painless, just the drives have different numbering but it was not a problem as all were individual volumes, no raid.