A roast in a dutch oven is going to be like pot roast. You would be using the cooker instead of an oven. Very moist cooking - more a braise, really. That's really a perfect use for a dutch oven.
Tie the roast, if needed. Season the roast, brown it on all sides, put it in the dutch oven with some liquid (wine, stock, water, whatever). Don't put the veggies in until later, if they're for food, not flavoring, or they'll be overcooked. The roast will benefit from the addition of some onions (just cut them in half and stick them in the pot). Lid on, put on the cooker at a mid heat.