How prudent is it to install lock on grips onto carbon fiber mountain biking handle bars? Are there some grips that will work and some that won't?
You need to check with the manufacturer of your bars (and the grips you're choosing), but in most cases its not a problem. As with all things carbon fiber, don't over tighten anything.
Some manufacturers have specific grips which are marketed as carbon fiber friendly. For example, Easton's lock on grips are marketed as being friendly with carbon bars.
Note that this is a bit different than using bar ends - Ergon notes that their bar ends are not safe for CF bars, but their non-bar end grips are safe for CF bars (they also have some suggestions on what to do if your grips slip).