If the meat will fit and you have room for airflow around the butts, technically it will work. However it will take a long time as that is a lot of mass to get up to 195-205*. If you are going to smoke at say 230*, I would probably start the empty MES at 275 or even 300* and set to desired temp once the meat is in. That will help a little with the shock of that cold mass of meat, but it's still going to be a load on the smoker.
I with Jimmy J on this one, I also doubt you can get 4 ten pound butts in a 30", but I may be wrong. You want some space between them for air flow (think heat flow as well) and a path for smoke. Anywhere they are touching, you will not get smoke flavor or "bark" formation.