Per Konstantin Shemyak:
Now, if I like the hub and decide to build a bike on a new frame,
it will be the frame with Rohloff-specific sliding dropouts. (I do
not want a chain tensioner, and horizontal dropouts are rarity
nowadays; also wheel removal is easier without the chainstay lever.)
Can the non-OEM hub be directly used in OEM dropouts?

I'm not sure what "non-OEM" means, but if your hub has the longish torque arm
that hose-clips the a chain stay I'd say the answer is "yes".

What you're looking for from Rohloff is something they call "SpeedBone". It
allows using the disc brake mounting holes to perform the torque arm's function
- yet still allows mounting a disc brake.

Be prepared for a little sticker shock though... it looks simple, but it's not
cheap.
--
PeteCresswell