Is dermographism an isolated condition or a sign of many potential autoimmune disorders?

Not autoimmune. Dermographism is a common type of physical urticaria (hives) and unrelated to food and environmental allergies. It is not related to autoimmune disorders. For a brief review, go to my blog at: http://www.Familyallergyasthmacare.Com/2013/05/dermographism-i-scratch-therefore-i-hive/.
Hypersensitivity. Dermatographism is a hypersensitivity to mast cell degranulation in the skin from contact. You can write your name on the skin witha blunt object and then it will get red and raised as the inflammatory reaction develops. A supplement like d-hist with quercetin, which is a potent mast cell stabilizer may be of benefit without side effects of antihistamines like drying, sleepiness, etc.