Yes, you can overcook stew meat in a Dutch oven but it's pretty rare to have overcooked stew meat. Make sure after the 2nd hour of braising the beef stew to check it every 10 minutes until it's perfectly tender. Once it hits that tender stage it can move into a tougher drier stage if you overcook it by 15+ minutes. So you can see you have plenty of room to make sure your beef stew is perfectly tender. It doesn't overcook in a few minutes or anything that stressful!