As a pretty big fan of Mel's playing I'm ashamed to say that I had never heard the name "Rub-a-Dub". I immediately recognized the sound and concept when I heard it, but I didn't realize that Mel had given it a little onomatopoeic name. It's a pretty simple concept, and a clever way of seamlessly making ensemble hits be it in a big band setting or over a solo vamp. When done right, it sits in this beautiful space where it's busier than general time keeping, but isn't full-on Buddy Rich. It's the best of both worlds, and depending on how you play it you can lean more heavily to one side that the other.
The other beauty of it is that although it is born from a pretty specific style, the idea is extremely applicable to other ways of playing. Straighten out the 8th notes, and you're well on your way to a very cool ECM sort of sound for starters. Anyway....
The basic sticking looks like so:
LRR = Rub a Dub
Voiced on the kit, keep the left hand on the snare and the right on the ride cymbal (at least to start). This is what allows it to feel simultaneously like time playing and soloing.
The first of each right hand is also played on the bass drum. This is where most of the hits should fall.
From there, you can start moving the left hand, or the second right around the kit.
Chris gives a far better explanation of it than I have, and he plays some great examples, so be sure to check out his video, as well as Todd's posts taking it a few steps further. Chris wrote out the ideas on his blog, but I knocked them into Sibelius so I could print it out for some of my students who will really benefit from it. I am, of course, happy to send anyone a copy if interested. Just drop me an e-mail.
Definitely check out the rest of Chris' "The Drum Hang". It's a brand new blog - only seven posts so far - but he's putting out content pretty consistently and it's all great stuff.