So I think I know the answer, but want confirmation.

If the target of vaders (upgrade card) crit has an evade token, can it be used to avoid the damage?

I am thinking no, as It is after the attack is resolved, but want confirmation.

"No" is correct. Vader is not an attack. The combat sequence does not apply. He deals damage.

As mentioned there is no "attack" from Vader that the target can negate so it will suffer a critical damage. That generally means losing a Shield token if one is available or being dealt a face-up card from the damage deck.

Crewman Vader works just like a large number of other damaging effects that happen outside of a direct attack. In general none of them are defendable in any way but most still cause damage just like normal attacks; that is to say they will remove shield tokens before dealing cards unless the effect specifically says it deals cards.