I have a Synology DS920 and installed Home Assistant using the VMDK image found here: Installing Home Assistant OS - Home Assistant (home-assistant.io). I think this is the only officially supported method if you want Home Assistant Supervisor and the add-ons.
Home Assistant Supervisor is included, so all HA x64 add-ons also work. I use a GoControl Z-Wave + Zigbee HUSBZB-1 USB stick connected to the front USB port of my Synology and it works with Home Assistant. Just make sure to expose the USB device in your VM.
There are a few negatives to using a VM for Home Assistant, which is running HA add-ons on top of your Synlology Docker install. Home Assistant startup times are incredibly long, I’m talking about 20+ minutes long. I only reboot HA at night because of all the disruptions it causes while offline during the day.
Home Assistant runs a little slower than my laptop w/ core i5 3rd gen CPU. Pages are not as responsive, but the dashboard responds to button presses fast enough. The slowdown is noticeable, but not annoying enough for me to do something about it. I’ve also noticed my motion light automations tend to run 0.5-1 second slower than before, even though I’m using a USB Z-Wave stick and all automations are processed locally on the Synology.
The VM also eats up a good amount of RAM too. I have a total of 8gb RAM installed on my Synology and I dedicated 3gb to the VM.
In the end, I’m seriously considering moving HA to a dedicated Rpi4 to offset the workload on my Synology. I run Plex and a number of Plex-related Docker containers on the Synology and may want to keep my Synology focused on that.
Good luck with your setup!