What if you type in your keyword in google, and no google ads appear. Does this mean google won't allow it? Or you have scored a good niche? Seems either peculiar or too good to be true. Are google ads ever down?
Depending on the word, it might just be that nobody ever searches for that keyword. I suppose if that's the case, there's no harm in trying it out then. I know sometimes Google won't show your ad for a keyword that has extremely low traffic...
you can do phrase matching using " " marks or [ ] around your group of words. look HERE for a little more info on what the difference b/w them are.