Thus Spoke the Sixth House

The dialogue of many unique Sixth House members suggest you were meant to speak with them first, then fight if you so chose. Especially since many of them will go on to acknowledge your right to the first blow as challenger, as is House Dagoth's tradition. I found it obtuse to have to cast a calm spell or sneak up on them to talk. I've fixed that for myself, and share it here for anyone interested.

All ash vampires except for Dagoth Gilvoth will no longer attack you on sight. Gilvoth's dialogue points to you forcing a break in the fight to chat, which Gilvoth won't have any of. I think it fits his character to be hostile to you. Dagoth Ulen and Dagoth Uvil in Kogoruhn will also let you speak with them, since they both have unique dialogue. Dagoth Gares in Illunibi is an interesting case -- he's hostile on sight, but will force dialogue with you at a certain distance. As soon as you exit dialogue, he'll resume attacking. This felt strange to me, and didn't agree well with the things he said, so he'll still force dialogue with you, but only attack in defence of himself.

Install by putting the esp in your data files, then checking it in your load order. Cleaned with tes3cmd.

If there are other members of House Dagoth with unique dialogue (no, not counting the dialogue all specific ash creatures share), please tell me and I'll update the mod.