Use Starwind to convert from IMG to VMDK (export as VMWare ESX Server image). It will create two files, one VMDK and one VMDK flat. Upload the two VMDK files to the datastore. Create a new VM in ESXi, add a new, existing HDD, point to the VMDK without flat in the name, finish setup, start the VM, let it boot until you see "Booting the kernel" message, then go to Synology Assistant and install on the freshly created DSM (it may take a few minutes until it appears in the list). Over.
Thanks! I've managed to boot it and install DSM! Just this kind of step-by-step guide a newbie like me needs.
I've added a couple of VDs but DSM doesn't seem to be able to breate a RAID group or even format them. Any ideas on what I'm doing worng?