Here's the relevant part of the rules for werewolves and vampires:
10. Vampire and werewolf characters are a potential possibility, but this is similar to the weapon rules where it's going to be based more around role playing than stats. People aren't going to react well to finding out their companion could turn into a flesh hungry monster at any minute, and many of the religious, paranoid, or sensible types will likely try to kill them for it on the spot. If you do decide to go this route, your application will face higher levels of scrutiny than others because we need to make sure that you can actually properly role play somebody who is struggling to control their disease and accept that if it's discovered, they face a very difficult road ahead.
This, plus what Witty said, is definitely something for consideration, and of all our years GMing Elder Scrolls game, this game is the first one where we trusted a player's intentions for having a character be a vampire. Unfortunately, way too many people really just treat vampirism and lycanthropy like it's just a skill buff or to be a badass character instead of treating it like it's the infliction it actually is. Characters with lycanthropy are constantly battling a feral side of themselves and the knowledge that every full moon, they will transform against their will and be a mindless beast that only wishes to kill and consume. The Companions seem to have means to control their transformation, but even so they have to remain constantly vigilant not to let their beastial nature consume them, and many like Kodlak Whitemane wanted to be cured of it because anyone who is a werewolf is promised to Hiricine and can never reach Sovengarde, making it something of a crisis of faith. Some relish this condition and see it as a gift, but more often than not people end up as hermits, recluses, and generally avoid civilization because they can't live with the idea they'd kill and consume another person. It's seriously a fucked up predicament.
Basically, it comes down to we scrutinize sheets with vampire and werewolf submissions because we really are concerned about roleplaying and character building, not mimicking a video game.