hi,
I want to share my experience with you here.
I initially installed my xpenology on ESXi with .vmdk virtual disks.
it worked but I found the system a bit dusty when it's on a very recent HP Proliant MicroServer Gen10.
Then I had to re-install this one, on this occasion, I ran the disks in RDM and not in virtual. (direct presentation of the physical disks to the virtual machine)
the first advantage is that Synology is now in charge of RAID (there are no RAID monitoring tools on this server under ESXi so it's scary) and now Synology is 'not complaining' because there's no data protection on the volume :-)
the second advantage is that in terms of performance, it's day and night. There's no comparison with before, everything opens faster, only happiness.
and sincerely, the configuration to do for RDM disks is really simple once it is well understood.
Have a nice day.