Yes and no. You can definitely swap in legs or quarters, and if you want the dish leaner you could use boneless skinless chicken thighs, which will both hold up well with the longer cook time. A whole chicken may take a little longer, but will also give you delicious, tender chicken. If you want to use skinless chicken breasts then either swap the onions for onion powder or sauté them first. I've used boneless chicken breasts before and the cooking time is much shorter, so the onions simply don't have enough time to soften.