I've tried quite a few different floppy drive configurations over the years and from what I remember, the universal 400K/800K ROM works with all environments regardless of whether you have a 400K or 800K drive installed.
If you have an 800K drive installed in the system and your environment doesn't support double-sided disks, it will just behave like a 400K drive, so it shouldn't ever be necessary to install an actual 400K drive if you don't want to.
I'm not sure if an 800K drive works as a 400K drive with the standard 400K ROM installed, but from what little I now about the floppy interface, I don't see any reason why it wouldn't.
You do need a special driver to get full 800K disk support in LOS, but as I said before, an 800K drive will work just fine without the driver; you'll just only have access to 400K of the disk. I'm not sure if the driver works for all versions of LOS; I think it might only work with LOS 3.