For chili con carne, can you brown the ground beef, onions, peppers, etc in a crockpot (without the lid on) and then add the other ingredients to finish by slow cooking?
It is possible, but only if you have the right type of crock-pot. Most crock-pots are not designed for searing and as such do not get hot enough, quickly enough to sear the meat properly. You also run the risk of cracking the ceramic pot due to uneven heating/cooling as you add the meat.
There are specific models of crock pot with a sear function. If you were to try, I would recommend that you get one of these.
Another option I've owned in the past is a slow cooker in which the inner removable pan is non stick metal. This was specifically designed to be used on the stove for browning before slow cooking.
Overall I prefer the traditional ceramic pot as the heat is much more even in normal use; the lack of a handle on the metal pot was also annoying for browning.
I have several crockpots and none will brown ground beef, onions, or peppers. I recommend using a frying pan instead.