Yes it's safe to slow cook raw chicken.
The slow cooker will slowly cook the raw chicken until it's fully cooked and it will make the meat on the chicken softer and easier to chew and digest.
I make soups with chicken and place cut up chicken directly into the slow cooker when it's raw and then in 8 to 9 hours when I'm ready to eat the food or serve it the chicken has fully cooked.
You can also place raw chicken in the slow cooker when it's on the bone such as chicken legs, chicken breasts etc directly into the slow cooker and it too will cook just fine.
The slow cooker will do the cooking of the raw meat including the chicken.
But you can brown the chicken or cook it partially before putting it into the slow cooker if you want too but it's not required.