Can Plecos tolerate salt ?

Salt is added to aquarium to improve the slime coating of fish and to prevent parasitic infections.  Many aquarium fish tolerate salt. 
Plecos too can tolerate salt by to a very small extent about 1 tablespoon/30 gallons.
Plecos are generally more sensitive to salt than other fish. 
If you have plecos in your aquarium do not add salt to it.  The risks outweigh the benefits, if any.