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.

Angelfish are tropical fish while Gold fish are cold water fish.  Goldfish require much lower temperatures.  While many aquarists keep angelfish along with goldfish without any problem.  While some  aquarists successfully keep goldfish and angelfish together, sometimes angelfish can attack the goldfish resulting in death or damaged fins.  

Compatibility depends on the temperament of the individual fish. 

Goldfish also generate huge waste which can contaminate the water quickly.  This, however, can be addressed by changing the water more frequently.

Hence, it depends on the individual fish.  It is not advisable to keep the two species together.  If you must, you can try keeping them if you have a big tank where each fish can keep to its own area with lots of plants.