Do you mean "sulfa" drugs? The answer would be No. Not the same as sulfur, even though sulfer is the base element. Sulfer can be found in a wide range of foods, hard to avoid. Here is an excellent article of the difference between sulfur, sulfite, sulfa, sulfate, ... https://allergies.about.com/od/medica...a/sulfahub.htm
He would probably not be allergic to the sulfur itself(that would be wicked), but might be allergic to MSM. Being allergic to the sulfa drugs, would not be the same as other compounds in the drugs are causing this. As far as its use with arthritis, many people are pleased. But also there is a lot of hype surrounding MSM. MSM is synthesized from heating DMSO to oxidize it. DMSO is also popular especially with livestock. If MSM doesn't work for him, try to rub some DMSO on the area, after cleaning it.