Yes the salinity is ok from my understanding the absolute ideal for brackish is 1.008 though. Before buying the eel find out the salinity the shop has it in. It is better to place fish suddenly in lower salinity than higher. The Gymnothorax is a very hardy fish and the only problem you may have will be getting it to eat. They tend to go on hunger strikes.
What size is your tank? The G Tile get around 2 ft so if the tank is not something you may want to upgrade later you may have problems anytime they are moved. Just keep this in mind.