Yes. Many people have taken "sulfa" drugs (usually an antibiotic) and have had allergic reactions to them (usually hives). This does not mean they are allergic to all medications containing the element "sulfur." for example, you may be allergic to sulfamethoxazole (an antibiotic) but not to hydrochlorothiazide (a sulfur containing high blood pressure medication).
No. Those are two words that are generally used to refer to the same thing.