I've found advice on the Web for modding the original ModDB version and the Steam version, but half the mods they recommend don't work for me with the GOG version. Some recommended mods that don't work at all for me are:

Oblivion Reloaded 6.5 and Oblivion Reloaded Combined
Vacuity
Nehrim Character Overhaul
Oaristys' Revamped Nehrim

I'm using MO2 for modding, but I doubt that's the issue. I've used it extensively for modding Oblivion, and verified it's creating the correct file structure for Nehrim. But still no joy.

They should work; the issue is likely one of file dating leading to archive invalidation. Did you follow the advice here to a T?

https://www.nexusmods.com/oblivion/mods/45554?tab=posts

Thanks. I somehow missed this reply until now.

Yes, I followed the instructions referenced. And MO2 handles archive invalidation automatically (as long as you check the relevant option, which I did).

FWIW I recently discovered that some OBSE mods (e.g. Display Tweaks) work for me only if I install them manually, so maybe that's the problem. (With Oblivion, those same mods work fine when managed through MO2.)

Regardless, the game's working and I'm enjoying it so I can live with the vanilla faces.