You can mount a suppressor on anything. The question is, would it cycle? And in the case of a Rohrbaugh, would it overstress the gun?
Suppressors work great on fixed-barrel guns, where there is no cycling issue. Locked-breech guns without a tilting Browning-type lockup will also work reliably. Tilting barrels frequently have problems...and I suspect that a Rohrbaugh has the barrel tilt through a longer angle than a service-sized pistol. This is why there are quite a few suppressor manufacturers who are making recoil boosters.
Overstressing? Possible, but I don't have the design details.
If I were doing it (and I might be), I'd go with a wet can. Something along the lines of an AWC Abraxas...relatively light and compact. Hopefully enough so to avoid needing a recoil booster to function. There isn't much point in putting a suppressor the size of a tube for paper towels on a gun as small as a Rohrbaugh...it kind of misses the point. You're looking for a total package that is still small.
In any event, I'd be up for a threaded extended barrel.