Pretty much this, I'm certain vampires are involved in Skyrim. Why wouldn't they be? If vampires could infect the Nerevarine, why not the Dragonborn? He's still a mortal after all.
Even if this is an April Fools joke...it's vampires. It would take no time at all to put them in, and they've been in since Daggerfall. It's practically a staple of the series. I don't even think it's something to be concerned about.
Vampires are one the least complex things to add to the game, so why would it be an April's joke? Vampirism has featured in every single TES game, I'm pretty sure it'll feature in Skyrim as well.
When I started Oblivion (My cousins convinced me) I rolled a Lizard (They told me after I picked him that it was nearly impossible to become a vampire with lizard).
The first time I slept BAM VAMPIRE, second time I slept (Cured my disease by then) BAM vampire.
It is like they are stalking me.
Anyways I want a werewolf to attack me out of nowhere (It is going to freak me out and be a hilarious experience) and turn me into a werewolf so I can kill those vampires werewolf style.