I don't see why you couldn't use the crock in the oven.
My very first crock had an all glass lid.
All the ones since then have a hard, plastic knob handles. I have very nice pots and pans and the plastic knob handles on the lids go in the oven just fine. But, the skillets can't go in the oven because of the handles. You would think the skillet handles would be move oven resistent than the lid handles.!
I use those liners all the time. Makes clean up a breeze! Won't go back to using the crock without them! I do spray them with cooking spray, found out the hard way that food really sticks to it and lost good size chunks of meat.