Eladrin armor adds to the maximum distance of any teleport you make. Dimension Warp (Swordmage Utility 2) lets you basically 'castle' with one ally (or castle two seperate allies) within a close burst 3.
Um... wow. First thought would be that it doesn't have an effect, since you're not going for 'distance' here, but rather are swapping around allies (or swapping places with an ally).
Second thought would be that if it does apply, it would have to be to increase the burst (since you can swap around allies further away), but that would be increasing it by one square on each side of you, doubling the power of the armor.
Third thought is that this is a good thing to fix before Forgotten Realms is published.
EDIT: Fourth thought - whether you're teleporting yourself and an ally, or teleporting two allies, Eladrin Armor only adds to the maximum distance of any teleport you make. It doesn't add to the distance that you can teleport other people, does it? If it doesn't, then it doesn't matter how much further you can teleport, you can't pull the other character back that far, so the power would fail if you tried to swap places with someone 4 squares away - you could port that far, but the power would only let you port them back 3, and that's not how the power works. Ditto for swapping around two allies. So i'd say the power doesn't interact with the armor.
Or maybe that's too strict an interpretation of "any teleport you make"...
I'm surprised that this question hasn't already come up via the paladin power "Benign Transposition."