Slap isn't a "tone", it's a playing style. Usually it demands a very consistent fingerboard, straight neck, and low-ish action (at least if you're an "advanced" slap player, if you're just doing thumb-pluck then the action doesn't matter so much, as long as it doesn't tire out your hands). To answer the question being posed, IMO the "feel" of the instrument is much more important than the tone from the pickups. The tone can always be changed by the preamp and tone controls, but the feel is a part of the instrument and can't be changed. That being said, I prefer thin and perfectly flat necks, and maple fingerboards. My new Roscoe LG-3005 is one of the best slap basses I've ever owned, it's perfectly consistent, in terms of string balance as well as physical balance, it has a maple board, and a myrtle body, which is nice and heavy, giving it a solid and resonant fundamental. The 35" scale helps too, it's very comfortable for my largish hands. It took me about an entire day to set it up correctly, but once that was done I was completely blown away by how comfortable it is. I can slap all day and not get tired, and it's laughably easy to do machine gun triplets and all that. I put a little Jasco lemon oil on the the back of the neck about once a week (Ron at Alembic recommended that to me years ago, it works like a charm and I do that on all my basses), which makes it a little easier to slide my thumb around where it has to go. The Roscoe neck is extremely comfortable, very easy to play for long intervals, and also very easy to move seamlessly between slap and fingerstyle (that's where the string balance becomes really important). All IMO of course.
The man's a genious, and I think anyone that uses any slap technique owes him a debt of gratitude.
