Me personally, I dont think Snape works for anyone really. he only works for himself.
Yes, I do think that Dumbledore is really dead. Rowling said in an interview that it was necessary, because the hero always has to face the villain alone in the end. If Dumbledore would be there holding his hand all the time, it would be way too easy.
About Snape - well, I would hope he turns out evil, but sadly I do not think he will. If you think back to the circumstances - Dumbledore knows that the Order needs Snape as he is the only one that can give inside information from the Deatheaters. This is worth so much, much more than anything Dumbledore could give. Dumbledore knows that to keep up the appearance of Snape working for the DEs, he HAD to take the unbreakable vow - and that Dumbledore has to be killed, else Snape dies. And DD knows that Snape has more worth at the moment due to his position. Also, Dumbledore did not fear death (several examples where he said so in the books)- so why on earth would he start pleading the minute it looks like Snape is going to kill him? No, Dumbledore pleaded to ask Snape to DO IT, not to chicken out, because it had to be done. The look of hatred on Snapes face described in the book is in my opinion either for Voldemort, or
really for Dumbledore because Snape hates to do what DD makes him do.
So I suppose Snape is on the good side, but still a really selfish nasty git.
(he is my fav. character
)