AFAIK, the kobold just need to roll a 20, doesn't matter what save it has if it has evasion...
Same thing with the monk or rogue... CR50+ monsters casting chain lightning, the monk (2+ levels) or the rogue (2+ levels) roll a 20: Save... 0 damage...
(and of course the CR50+ monsters will spam it until you fail)
(again, you wonder why some monsters like disintegration, since even on a 20, it does some damage)
Also, I have seem three '1's in a row, but never seen three '20's in a row. No Dice?
I don't think there is an ED ability yet that let kobolds fail on a 20 because it failed to match up to your DC...
But there is one for save on a 1 if the character' saves are high enough...