No, E minor is not the relative minor of A major. It's the relative minor of G major. The rule for finding relatives is to take the major key and go down by a minor third.

The relative minor of A major (easy to figure out with that rule) is F# minor.

EDIT: Just from the first few lines that site looks like crap. The writer says that you can play a certain minor scale over a major chord and it fits, and it's the relative rule but he "can't explain why". He also said "just go back two letters" to find a relative minor (keep in mind he would have ignored the # in F# minor) and somehow ended up at E minor.
Last edited by :-D at Mar 6, 2008,