With an ISD II that has Avenger title and Overload Pulse if I role a blue crit does that trigger the Overload Pulse and then per Avenger title no exhausted defense token can be spent? So essentially a blue crit with this combo can equal no defense tokens for one attack?

No. It doesn't work because the timing is wrong. The steps of an attack are:

1. Declare Target (including measuring range, arc, line of sight etc.),
2. Roll Attack Dice (gather the initial dice, remove dice if obstructed, roll them),
3. Resolve Attack Effects (add dice, re-roll dice, spend accuracies to lock down tokens etc.),
4. Spend Defense Tokens (this is where the defender spends their defense tokens, and where evades and scatters do stuff),
5. Resolve Damage (the attacker has the option to resolve a critical effect, then damage is suffered).

So the defender spends their defense tokens in step 4, but the Overload Pulse doesn't go off until step 5. Braces and Redirects haven't done anything by this point, but the tokens were still spent, so they still have their effect as normal.

To pull off Overload Pulse-Avenger you need either a second ship with Overload Pulse to shoot first (triggering Overload Pulse, so when the Avenger comes to shoot the defender's defense tokens are exhausted), or to get a double-arc with Avenger; the first shot (ideally the side) triggering Overload Pulse, then the big front arc using Avenger (it's an exhaust now, so only works once) on a defenceless target.

The more common option is Boarding-Troopers Avenger; Boarding Troopers happen when the ship reveals its command dial, so before the attack. It only works for one round, but doesn't rely on getting a lucky blue crit.