LOL - a lot depends on your slow cooker! Some will say you can use frozen chicken (if you use the high setting) - some say no way José. Read the instructions that came with your cooker - they will tell you what is safe, and how to do it if possible, in your particular "pot". If your instructions specify only using "thawed" chicken - then no, it would not be safe.
"It ain't what you don't know that gets you in trouble. It's what you know for sure that just ain't so." - Mark Twain