After some research and asking around, it seems that pretty much only southern mechanics have ever heard of rubber freeze plugs. They are pretty much not used in the north because of the extreme cold temperatures that render them pretty useless. Here in Georgia, the lowest it gets in winter is MAYBE 30 degrees, with most of the coldest days being around 40. They are able to be put in without removing the block, and they withstand the pressure of the coolant system. Although rubber, they feel extremely hard, almost like an incredibly hard plastic. I had no idea that no one would have heard of them.
The reason a rubber freeze plug was put in was because they couldn't find the original freeze plug, even at the local Chrysler dealer.