Pretty much. Frank Schaefer reports that dumping marine-acclimated scats into a freshwater tank only causes them problems with buoyancy since it takes a little time for them to adjust their swim bladder to the different density of freshwater compared to the sea.
Personally, I'd be a little kinder. Put scats in a bucket, half filled with fresh/brackish water. Add salt water in stages over the next 30-60 minutes. Then remove scats, add to marine aquarium. Have done this with brackish water fish many, many times.
Monos are temperamental fish, and adults can be notoriously sensitive to travel. I think it's an oxygenation thing rather than salinity. So you're best off buying fairly small monos if you have the option. Juveniles are perfectly happy in saltwater.
Cheers, Neale
Apparently, from what I've read on here just dump them straight in

.
They are true euryhaline fish that are fully adapted to going from one extreme to the other so acclimatising them is a waste of time.