Some of the links on this forum allow SMF, at no cost to you, to earn a small commission when you click through and make a purchase. Let me know if you have any questions about this.
Few weeks back had 2 trimmed racks of spares, the skirts from the spares, a good size pan of Wicked beans, and 2 family packs of chicken leg quarters. I would think you should have plenty of room to do 3 butts on each rack if you have a 22.5" WSM, a 18" might be a squeeze.
I read somewhere that people have done that the other way around, to use pork-dripping tastiness to keep the brisket moist. No idea if it actually works like that but I read it on the Internets so it has to be true.