From the DiMarzio website.
"Unlike traditional Js, each Model J™ is individually humbucking. It's not a stack: each coil picks up one pair of strings. By doing it this way, we keep the resistance down, and the tone clean and clear."
DiMarzio Model J™ | DiMarzio
So they are split, dual coil. This is similar to a p-bass split pickup, but in a single housing and not offset.