I wouldn't think so. It will blow air, but it won't do much to degas the mead. You're much better off with simply stirring with a sanitized rod/dowel/spoon.
i dunno.
it depends how much vacuum it can create. depends on what type of pump it is.
if it does create vacuum and can handle the flow of co2 produced, then it will be great as you can leave it running for a long time.
just make sure the carboy can handle the vacuum. you could always fit a vacuum switch to turn the pump on/off.