They obviously put flopper and mule kick there for a good reason, that they will be making a return to Zombies. Then only question is when. I don't see it happening before the next map pack tho.
I have tried many times to see if I can interact with flopper and mule kick, using both then retriever and redeemer, but to no avail.
Treyarch is just toying with us and getting people to come up with theories until they decide to bring it back.
As for the crane, I don't see it having anything to do with the perks other than treyarch letting us think we can get them.
Obviously I may be wrong, but that is just my thought.