So i couldn't explicitly find anywhere in the forums or the strategy guide whether or not vampirism sneak stacks with the sneak perk? The first one in the tree where you increase the harder to detect%, and then vampirism which gives 25% harder to detect. I wanted to assume it stacks but i was just wondering if anyone knew different?

You couldn't prove it by me, but the way everything else is in Skyrim, I would say yes.

Generally everything stacks; main exception is potions, they stack with other buffs but if you drink a new the old is canceled. (This is unlike previous games)

So for stealth, both perks, the skill, abilities like the vampire sneak bonus, sneak enchant and one portions stacked. If we had an fortify sneak spell, (easy to make in the CK) it would stack to.