CAUTION: Very long post and possible spoilers.
We all know the properties of a Zoan type DF. We know that it it gives the user the ability to become one specific animal. We also know that they can be "fed" to inanimate objects, where the fruit creates life in the object (in the cases of Funkfeed and Lasso); this was one of the discoveries made by Dr Vegapunk's experiment.
This leads me to my theory. What if Zoans can be used to raise the dead, or at least partially. I mean, if they can be "fed" to none living objects, can they not be "fed" to formerly living things like corpses and skeletons. So far we have seen that the objects possessing zoans, when in there hybrid mode, retain some of the properties of the object have; and they also have both full object mode as well as full animal mode. If this was applied to a corpse, could some of the properties retained, besides appearance, include memory, fighting abilty and speech, making it no different than a Zoan fruit user in their hybrid form. Also when in the normal form (as a corpse or skeleton), I theorize that they would be able to move freely of their own accord, based on the belief that the only reason Funkfeed did not move in it's sword form was because it lacked self-movement (which humans don't), as it had to be conscious to know when to change forms.
The second part of my theory is to do with the fact that the user is dead, and if something is dead it can't be killed again (I guess). If the user is re-animated in this form, then they are technically half-dead, making them undead (speculation). If this was the case then they should be immortal in that state, as they can't die a second time (more speculation).
The thing(s) that lead me to this belief are as such. I was curious as to why CP9 (employees of the WG like the Marines) had so many zoan types. After Coby explained about Vegapunk, I started to think that he, Vegapunk, was the one who Zoan-ised Spandam's sword, as well as being the connection Spandam mentioned that provided them with the Zoan DFs, seeing as he must have a few to use for his experiments. If my theory above is correct, then Vegapunk could be trying to create Marine super soldiers, from fomer marines. e.g. If a marine officer of great power without a DF (Garp?) died while in service, then they could be revived not just with more strength coming from the DF, but also with possible immortality. On a side note this could be one of the theories that explains the existence of Brooke Funny-bones.
Please discuss and comment (constructive criticisms are also greatly encouraged).