Yes, you could use a small whole chicken in the slow cooker for this Thai sweet chili chicken. To do so, place the chicken in the slow cooker and then brush it with the sweet chili sauce. Then cover and cook on low for 6-8 hours or 3-4 hours on high. To make sure it's cooked, use a meat thermometer to ensure the internal temperature has reached 170F/76.7C. You can cook the chicken with or without the skin.