It depends on the compressed length of your shocks. If they are any longer than stock length when fully compressed then yes because without them the shock will bottom it before your axle hits the bumpstops which will cause your shocks to blow and start leaking.
I have 2 inch extended rear shocks and extended the bumpstops 2 inches as well and when fully compressed I only have about a 1\4 inch shock shaft exposed.
Seeing as toytec includes bumpstop extensions with their boss kit, which uses the same rear shocks as their 3 inch kit, if you are going to be wheeling and really using all the available suspension travel I would recommend installing some extensions.