Its actually more about you then the monitor. Monitors are born to eat nasty old dead things.
If the mice were cool or still cold, there should not be a problem. But if they were hot, they will fall apart when thawed. Again, the monitor won't care, but you may.
About bacteria, all mice, frozen, refrozen, etc, have bacteria. The real question is, does that mean the mice will have a harmfull type of bacteria. No it doesn't. Could it? yea, it could, but so could live mice or fresh nicely frozen mice.
Remember, a healthy monitor can and do consume all kinds of nasty horrible rotting crap, without a problem. The key word here is "healthy". Also, another key is, proper temps. With proper temps they can digest a tank(not really, but seems like it)
Again Monitors, thrive around dumps and garbage tips. They consume and thrive off of human garbage. Which is most likely the worse kind. The question, is your monitor up to it. Good luck FR