So in regards to Krennic, I don't think he would work with the Onager even though measurement is taken from the targeting token. I think Krennic would only apply if the target is in the usual Medium to Long Range.

Eg. SCBT has Ignition Medium, so if the target would be just inside long range of the ship, that would probably mean the target is short range of the token, would the short range measurement from the token cancel out the ability to re-roll?

So in regards to Krennic, I don't think he would work with the Onager even though measurement is taken from the targeting token. I think Krennic would only apply if the target is in the usual Medium to Long Range.

Eg. SCBT has Ignition Medium, so if the target would be just inside long range of the ship, that would probably mean the target is short range of the token, would the short range measurement from the token cancel out the ability to re-roll?

Depending on how he interacts with this ship, he will be either good, or crap.