A little bit of glute, ab and thigh work comes into play in stabilizing the lower body, especially when placing the feet on a stability ball; however, to get a good workout in your glutes and hamstrings, your butt has to be higher up, pushing up so your hips are level with your chest. Doing this during a tricep dip would force the arms and shoulders into hyper extension, not a safe position. Try the bridge, which has a similar body positioning to the dip, to get that glute and hamstring work.