I really don't think that your neons would have/ could have killed your ghost shrimp.
Here's your information:
Temperature: 83F
Ammonia, Nitrite, Nitrate: Not mentioned
GH and KH: Not mentioned
Tankmates: Neons and Otocinclus (can I assume some snails?)
Types of "Ghost Shrimp": Two
First of all, there are a lot of species sold as ghost shrimp. If you received, what looked like, two different species then you may have gotten brackish and freshwater types. The brackish types would have died pretty quickly in fresh water.
Also, ghost shrimp (Palaemonetes paludosus) require pretty hard and basic (high pH) water for long term survival. So, if your water is soft with a low pH, that may have killed them. All shrimp also require very low nitrates and no nitrites or ammonia.
Thirdly, ghost shrimp sold as feeders (and those not sold as feeders) are often very poorly kept. This is because they're just going to be used as food and aren't needed to be kept alive in the long term. The shrimp may have just been in very poor health when you got them.
The last thing I would assume is that your neons killed them. Neons will eat baby shrimp, but would have a hard time taking down an adult ghost shrimp. Now, once the shrimp has died of other causes, that's another story. The neons may very well pick at a dead shrimp.
That's my opinion.
Sam