#1
I wasn't sure what to post this under, but whatever.

So lets say you have your capo on the 2nd fret and a tab tells you to play 2-2-0-0, should I play 4-4-2-2 (both 2's just being open) or is the tab written wrong?
#2
It's relative to the capo. So technically you'd be playing the 4th fret of the guitar, but it would be the 2nd fret after the capo
#3
If the tab mentions that you should have the capo on the 2nd fret then you should read the tab relative to the capo ie. if the tab says 2-2-0-0 you should play 4-4-2-2 but the capo plays its part by clamping all the "open" strings to the second fret.

Long explanation for your question... But yes as long as the tab mentions the capo or does not say otherwise.