If you can SSH to your NAS then go ahead and try (after backing up of course)! Quite a few NAS do support an awful lot of things; looking at my own synology, that has a dashboard where you can install web servers, MySQL, bulletin boards - all sorts really so it isn’t too much of a stretch to imagine FOG can be installed on the NAS. It all comes down to what flavour of Linux the NAS is running and how friendly it is to repo’s vs recompiling…