Thanks for the suggestion, Hickory. I tried using your console reset on the bridge outside the city before initiating any conversation with the gate guard, but the city is still hostile.
Did you see the drow scout run off towards the city just before you reached the gate? I'm just wondering if, by any chance, you managed to kill him. Since he is of the city, that may have caused the city to turn hostile. It's a long shot, because I'm not even sure if you can kill him. Other than that, I can't think why the city would be hostile before entering, if you have Adalon's illusion in place, unless... you gave the gate guard reason to distrust you. How did you answer his greeting?
Is the drow illusion spell supposed to alter the appearance of my party? The dragon said she cast it, but there was no change to my party visually. Could that be the culprit?
Your avatars do change their appearance to Drow in vanilla (I see you have the tweak installed from your other comment, though), but that is purely cosmetic and has no bearing on the hostility, or otherwise, of the city.
but the vanilla game doesn't alter your appearance (by my understanding).
Actually it does; see above.