I doubt if those 2 tangs will ever coexist in a 75 gallon tank. Sailfins get large, and need more space than a 75. They may live together for a short time, but eventually I'm sure the sailfin will kill the yellow. He will also be very stressed in a small tank. This could cause him to have some health issues, and become aggressive towards other inhabitants in the tank.
To address your current problem with the white spots, take a look in the disease forum. Sounds like a case of ich settling in.
As far as ***** goes, as long as people continue to buy fish from them, they will continue to sell them. IMO don't buy from them, and maybe eventually they'll stop selling.