I am not sure about everyone else but my crock pot even on low still brings product to a boil. It takes a while.
Ribs would proabably be pretty good in a crock pot.
I just did a beef stew on low for eight hours and it was excellent. It was plenty hot and I am certain no bacteria could survive in that temp. It had to cool a long time before I could sample. Your ribs will be plenty moist and soft. They might not have to cook so long. YOu can judge yourself as it goes along.
Paul E. Smith