I don't mean to resurrect an old issue but for anyone searching on this issue, I wanted to explain, as I work at an indirect verizon retailer. The reason most stores tell you that it has to be the "Verizon version" is that (at least with the system we currently have at my store) if the device's serial number is not in verizon's system, then the system will outright refuse to activate it as it's not a "recognized device". BUT, there is a workaround: if the sim is already active, then it can be put into an unlocked device and it'll work (providing it supports the networks you're trying to connect to). The problem here though is in the case of ipads, we get several people that come through with the ipad air 2 and as we're a small store, I don't have another ipad I can activate your sim in AND it would ruin the warranty on the ipad I use to activate it in.
Long story short, complain to verizon about their serial number lockout, they're the ones causing the issue, they just don't want people using devices that they didn't sell and haven't gotten the opportunity to load their software on!