I've come across many websites with listings of soy derivatives, here's a summary of hidden ingredients you may find in vegan foods.
Hydrolized (Vegetable) Protein
Mono and Diglycerides
TVP (textured vegetable protein)
Most people with soy allergies can tolerate many of these ingredients. Soy oil, for example, has a negligible concentration of allergens and only the most sensitive individuals will react. Vitamin E and MSG are also distant derivatives and won't give most people any issues.