A swivel will not change the action of a crank ... but it probably won't do a whole lot of good if the crank is looping because of speed.

Many crank trollers/pushers will have a swivel on the weight .... attached to the leader line the crank is tied onto (by straight tie or a clip). Others may have swivels on both ends of the leader ... or just on the crank (if there's no weight being used).

It's all in how you want to rig them up. Most cranks pullers/pushers I know use 2oz of weight & troll @ 1.8mph ... I usually push cranks &/or jigs .... and use 1.5oz of weight & troll at 1mph. But, I'm new to "pushing" and also don't have the trolling motor power to run much faster (for any sustained length of time). I'm more of a single pole jig slinger, and just "push" jigs/cranks when it's peak time for that type of presentation.