Yes, mostly Micarta knife handles and even Micarta knife handle scales are dishwasher safe. But getting bounced around by the water will dull the edge of your knife and the chemicals in the dish washer cleaner will attack the steel, even stainless.  The heat of dishwasher wont effect the material. As Micarta is known for its heat and cold resistance properties apart from being water resistant. Therefore, I personally do not recommend it ( chances of damaging the blade) but can be washed in a dishwasher.