Dunno what type of hermit you are dealing with, however, my experience with blue leg hermits was quite amazing. I tore out the sand bed of a tank and loaded it all into a large thick trash bag and set it in an unheated garage in winter. About 1 month later, it was time to start a new tank and I needed some substraight. I dumped this substraight into cold fresh tap water, let it settle, then dumped in salt untill it had the salinity I wanted.
Later that day, I notice I had at least 10 hermits cruiseing around the tank...
I dont know if all hermits are this tough, but I personally would worry at all about just dumping them in.