So I just got done testing it out myself.
I took a level 1 character and using him, I fast travelled around 20+ times between Whiterun, Riften and Riverwood since those were the most frequently attacked on my "legit" playthrough and all 3 were left as ghost towns.
I am overjoyed to report not a single vampire attack. None at all. Since this playthrough is a just for fun power-fantasy RP it means I don't need to worry as the character is stuck at level 1 with all skills maxed (so no chance of him levelling up and screwing the pooch so to speak)
Of course this is no consolation to the "legit" players (certainly won't refill my empty cities on my master difficulty level 70+ character) buy hey, it is a start I guess. Thanks for the replies guys and here is to my newly turne werewolf enjoying his new encounters, content and perk tree without having to worry about pesky vampires slaughtering his towns/cities

Edit: Of course I can't get the Dawnguard quest through rumors or guards but I found that just travelling there yourself means you can manually start it without issue. A small price to pay for my townsfolk staying alive methinks.