yep it stacks
But the question you really need to ask yourself is will my defence stop me getting hit when most ppl who pvp have 2 or more ACC enhs ?
Personaly my answer is no.
Stalkers can't stand and scrap, they work best in hit and run so powers like hover/manuveurs(which is only 4% def 3 slotted btw) won't really help in the pvp world.
Time for stalkers to think outside of the box 
Defiant's GoEH/MILITIS METUS
I love this this AT and I hate/love fighting against it... but that only makes me work harder!
We all know how to get around a stalker now but can the stalker pull something back?
Do the defensive attributes of powers like Manuveurs and Hover stack or help the Hide+Stealth combo?
My Regen stalker used to be quality, but he reluctantly admits, a respec would serve him better in today's stalk the stalker PvP experience.
Tips welcome, thx!
"Like War_Hero said, leave it as it is, it toughens up the softies." - Naz Nomad
Union Heroes
War Borg - Leader of The Paragon Knights
Union Villains
McCabe - Co-leader of The Rogue Knights
Defiant - Supreme Hero