I'd pitch them to be safe.
According to what I was taught in Home Ec many moons ago, frozen foods including meat meant for human consumption can be safely refrozen if the center is at least still crunchy, and it's still obviously very cold on the surface. I've refrozen meat for us if it met those guidelines and not worried, but then I'm the kind of cook who burns things beyond recognition, and chances are any bacteria that formed on it will be killed stone dead by the time I serve up the meat. (Don't accept a dinner invite here unless it's take-out
Since the feeders will be served uncooked, I wouldn't risk it. Even though it's a lot of money down the drain, replacing them is a lot cheaper than the vet bills. The thought of the snakes suffering would be enough to get me to pitch it.