One thing I remembered that is similar to your question about using the white dragonborn for dialogue. If you leave the dark urge's name as The Dark Urge there are a few lines where the narrator will say "You say your name, The Dark Urge, out loud" instead of "You say your name out loud" if you have a custom name. The first instance is when you awake on the beach after the intro scene. There might be more but I can't remember off the top of my head.

Are there special dialogue options if I choose the white dragonborn character instead of making a custom one?

Not sure on that one. I can't stand playing a character without darkvision. Preferably improved. I personally like drow since you get a fuck load of dialog choice good and bad so you get to decide what type of drow you want to be. For Dark Urge you usually get two different choices also. Either give in to the urge or push it away. Both are stellar story experiences.