Does the gunner (or luke skywalker (crew)) only activate when you roll all blanks (and or eyes) or can it activate if your target evades all your hits and crits?

The latter. Gunner activates if your target evades all your hits and crits. If, after evade, there is still an uncancelled hit/crit, Gunner doesn't activate. Let's take the following scenario:

You roll 2 hits and a Crit.

Your opponent rolls 3 evades.

Gunner activates.

However, Gunner only activates if you did damage, not necessarily to the target of your attack. What do I mean?

You roll 2 hits and a Crit

Your opponent rolls 2 evades.

A different ship activates Draw Their Fire.

In this case, it's still considered a hit because you did damage, just not necessarily to your opponent. Same thing with Chewy as crew. You did damage, even though it was cancelled after the shooting by that card.

It's actually has nothing to do with whether or not you did damage.

An attack hits if and only if there are uncanceled [hit] or [crit] results after applying defense dice and/or evade tokens.

An attack misses if and only if any and all [hit] and [crit] results are canceled by defense dice and/or evade tokens.

If they ever print a weapon that does not do damage when it hits (say it instead only gives stress tokens), it is still considered to have hit.

Likewise, there are plenty of ways to deal damage that are not "hitting" your opponent (Mines/bombs, asteroids, splash damage from assault missile, the ship that ends up taking the damage with Draw Their Fire).