Bloomquist plays against lefties, Reed against righties.
Bloomquist career against lefties: .272/.332/.362
Reed career against lefties: .169/.247/.228
Now, in terms of where they are and how they’re hitting this year, if you played Reed all the time you’d probably be just as well off — Reed’s better than where he was back in 04/05, and while I don’t have access to his minor league splits off the top of my head, it seems unlikely that he’s quite that helpless against lefties that his hitting would be reduced to Bloomquist levels. Still, this is defensible at least.
Anyway, so there’s data point one.
What really makes no sense though is Vidro. Historically, Vidro hits the same from both sides (seriously, the lines are within points of each other) — about a 800 OPS.
This year, he’s hitting almost equally badly from both sides — .215/.269/.312 vs RHP, .226/.250/.340 vs LHP (small sample size here, obviously) — and both Jose and Pepe are equally done. He is among the worst hitters in baseball against both left and right-handed hitting. Being a switch hitter just means he sucks from both sides of the plate.
Nearly everyone else playing baseball is better at hitting left or right handed pitching compared to Vidro. Clement qualifies as “nearly everyone else”. He’s a hugely talented hitter and even if you believe that he’s not as good against left-handed pitchers he cannot possibly be worse than Vidro in any situation at this point. Ever. Vidro’s done, he’s toast. Clement has a pulse. There is no situation you’d ever want Vidro over Clement, because in every situation of the other four hundred something hitters currently on major league rosters at least four hundred of them will be better than Vidro, and many of the three-hundred-some pitchers will too.
So beyond why you’d run a pseudo-platoon at DH with those two, it entirely baffles me why Riggleman would pinch-hit for Clement against lefties with Vidro.