RAW it allows it against both. Obviously you won't be able to communicate with the target, but think of it as the metamagic converting the spell into a sort of positive "vibe" energy field that makes the creature not want to attack you.
Mindless is part of their creature type traits, mindless, not their creature type itself, is what makes then immune to mind affecting spells. So this is exactly what you need to affect them, not to change their creature type itself.
Like if their was a metamagic feat that takes away a Devil's fire immunity, it wouldn't matter that it doesn't take away their Devil subtype (which comes with fire immunity), they went straight to the issue at hand.
Charm Animal doesn't work because while with that metamagic feat they're now susceptible to mind-affecting spells, they're not of the Animal type, so Charm Animal won't work for the same reason Charm Person wouldn't.
Charm Monster instead can affect them, as it works regardless of the creature type, and the metamagic bypasses the Mindless property.
Now personally I'd allow Charm Animal against Vermin because I find senseless the distinction between Animals and Vermin to begin with, as if insects and other arthropods weren't animals.
Right, I just came back because I realized what he meant by the type issue, Charm ANIMAL, duh.
Yes, agreed, Charm/Dominate/Hold MONSTER is generally what you need when trying to affect normally mindless/immune things with metamagic feats.