I would imagine the same safety guidelines apply to feeders as to meat intended for human consumption. If the food is at room temperature for 2 hours there's a good chance of bacterial growth that will taint the meat. If it never got that warm for that long refreezing is probably okay, although the proteins will degrage somewhat from the reforming ice crystals breaking down the chemical bonds between the amino acids.
A little bit of a chemical bond breakdown is a good thing, it makes the protein more bioavailable but too much means the protein is effectively denatured and not very nutritious anymore.
The Zombie Mama is here!