A compromise conclusion might be this - Be wary of slappers with high batting averages who don't bring something else to the table. Valuable slappers need to bring additional value with extra-base hits, walks, steals or ROE.
IMO what else they bring to the table is going to depend on where you bat them.
I don't know much about slappers, or the strategies employed to use them. Also, there seems to be several different flavors of slappers? Before finding DFP I always viewed a slap hitter as a glorified drag bunter. Now, I'm just confused (but learning)!
Most of what I'm reading here leads me to believe that slappers are generally: singles hitters, fast, smart, not many K's. Am I close? Not that there aren't exceptions, obviously, I'm just trying to define a very broad set of skills that apply.
So, where do you bat a low OBP slapper in order to maximize lots of balls in play with great speed and few K's? If what you're seeing isn't due to limited sample sizes, then a low OBP slapper should hit behind your high OBP that steals successfully (successfully meaning high success rate relative to the cost of being caught). Batting a slapper with a low OBP 1st because she's fast is the same mistake we've talked about elsewhere - sacrificing runs in the name of tradition. Put your low OBP slapper behind the base stealer with high OBP. My guess is you'd see her OBP go up (especially if you include ROE, which ought to be acceptable in this case as slapers put additional pressure on defenses) as defenses now have to worry about the runner at 2B.