If you did not add the food allergy info when you made the ADR, then, yes, you will have to call Dining to add the info.
Did you also complete the food allergy dining request form & submit it to the Special Diets staff? It is a form they have you fill out... you list the food allergies and all of your ADRs... they then use this to notify the chefs in advance. When you request the form, the Special Diets staff will also e-mail you all kinds of information about allergy-free products and where to find them throughout WDW... VERY helpful info!
Hope that helps, neighbor (I'm just up the road from you in Lombard!). If you have more questions, I'm happy to help. My 2-yr-old son is allergic to diary, soy, eggs, peanuts & tree nuts, oats, barley, wheat and rye. My 4-yr-old son is on a casein/dairy-free and gluten-free diet. We have found the WDW Special Diets staff VERY helpful.