There's no reason you shouldn't do it if
-- the little ovoid nub on the Rohloff fits in the channel without play
-- there is enough steel there to resist deforming the track end
-- you can arrange chain tension some other way.
The obvious way, on a Thorn forum anyway, to achieve the last requirement is to find an eccentric bottom bracket shell to fit inside the one on the Surly, plus a bottom bracket of small enough diameter to fit the eccentric bottom bracket shell. Otherwise you're going to be up for welding in an oversize bottom bracket shell: ouch.
However, there's another way, often used on bikes with track ends like yours and Shimano Nexus and other hub gearboxes, called a "t-nut", which allows the axle to slide in the track frame-end (what you call a "horizontal dropout"), thereby tensioning the chain. Bernd Rohloff didn't like this, presumably because it didn't meet his engineering standards, but a cyclist in a bind finds a way. I've never seen it done on a Rohloff but I have two other bikes with this arrangement, and it works, albeit not as conveniently and precisely as the expensively over-engineered Rohloff house design for sliding axle hangers, which Rohloff put in the public domain. Rohloff axle nuts are on a low-torque regime, so to provide positive location you might have to rough up the metal on the outside of the track ends a little (not inside the channel).
Note that chain tension, as long as it is on the loose side -- never, ever, on the tight side -- is less critical with a Rohloff than on any other hub gearbox I can think of. You're supposed to motivate a Rohloff with a much slacker chain than people cross-badging from derailleurs feel comfortable with. You may be able, depending on the exact dimensions of your bike, to arrange a correctly loose chain for all conditions of your fave chains with nothing more than a quick release half-link for even a full link. It seems to me worth a try.
Oh, for a time when even a small boy could understand and remember all the ins and outs of bicycles!
