I'll keep this quick and simple. Can a PC use the ritual stone, vampire raise dead ability and cunjeration dead thrall spells to summon a small army?

With the perk you can have two thralls... is that what you're asking? You can't go over that; possibly with mods you could. *shrug*

AFAIK, Yes. I've seen vids where the guy had quite a few zombie thralls.

I am refering to being a lazy mage whom contracts vampirism; the ritual stone, twin souls (perk) summon perminant atronachs or zombies and of course the vampires raise dead power. That's a total of 4 minions not counting a companion. It should be possible but I was wondering if anyone has tried.

I was ignorant of all this, and I've never tried. I can't imagine four groaning zombie followers. Sounds pretty annoying.

I love groaning zombie followers! I beleive before the 1.4 patch they would use monologue from their living battle cries when entering combat, that was annoying. Much better is "Mu-ust ki--ill".