In a medium bowl, toss the rhubarb with the sugar and let stand for 15 minutes, stirring occasionally. While the rhubarb stands, make the topping.
In a medium bowl, stir together brown sugar, flour, oats, cinnamon, cloves, and salt. Add the butter and oil and mix using your hands to gently squeeze the ingredients together until combined and crumbly, with some large pieces remaining. Set topping aside.
Using a large slotted spoon or spider, transfer the rhubarb to a large bowl and discard any juice. Add the blueberries, cornstarch, lemon juice, and vanilla and stir well. Transfer to a 9″ round or square baking dish.
Sprinkle the topping evenly over the filling, leaving a one-inch border around the sides. Bake for 25 minutes.
Reduce oven temperature to 325° and continue baking for another 30 to 35 minutes, or until the fruit filling is thick and bubbling.
Let the crisp rest for about 20 minutes before serving.