I finished playing campaign on Inconceivable alone right now, but because I played more horde/escape than campaign, I just assumed that you can extend cloak like Chain skill card (executing enemies), when it actually was only killing enemies.
If you have full upgraded Cloak, you can shoot and kill enemies without problem.
I know that few players play campaign for fun, I just did it for the achievement, but if someone else want to play, remember that Cloak works different than PvE Cloak.
I played 5 times campaign, and I just “discover” this on my last run (except if TC add another achievement for campaign (please don’t do it)).