Well lets see here. I have several bolt on basses and several neck thru models and can slap them all just fine.
I will admit that on my Alembics I had to clean up my slapping some. I credit this to the Alembics superior quality in sound. On my Alembic basses I have to raise my palm up a tad to keep it from hitting the strings. In other words, nothing gets by the Alembic. It is a much more sensitive instrument than the average bass.
It's like the first time you sing with an in ear monitor, or sing in a studio with headphones. You can really hear everything, mistakes in all.