Minor point of fact: The Imperials are capable of Ion Locking. Two Firesprays, one with Fletchette Torpedoes and the other/both with Ion Cannon(s). Alternatively, you could run a Shuttle/Firespray with an Ion Cannon, and a Rebel Captive for a single ship version. Or a bomber squad with Flechettes and Ion Pulse missiles...
The Rebels just have a slightly easier way to do it with R3-A2 on a Ion Turret equipped Y-Wing, though one thing to note about that combo is that the target must be in the Y's front arc, so running them together isn't exactly enough; positioning matters.
The tactic in question was not whether the Empire could Ion lock a ship, but could they unlock themselves. Only the Rebels can change the forward 1 maneuver to a green (R2 and Nien) and rid the stress to gain their actions back, Empire ships currently can't. They have no means to change their forward maneuver to a green maneuver
Ah, my mistake in understanding, thanks for clearing that up.