Should I precook frozen carrots before putting them into a crock pot soup?

No, there is no need to thaw them. Frozen veggies are bad in dishes that are being cooked fast ie. sauteing or grilling because they cause the temperature of a hot pan to decrease quickly but a crockpot is slow cooking so it will have plenty of time for the temp to rebound. Thawing them beforehand could actually cause excess water and residue.