If you do some research, you'll notice an insane amount of year-to-year variance in the league's overall numbers with RISP. What you'll consistently see, however, is that the high OBP teams, due to sheer volume of RISP opportunities, tend to score more runs, even with inferior overall SLG% to the low OBP teams.
This lends credence to the idea that, in general, there is a direct correlation between on base ability and runs scored. A comparison between the 2013 Red Sox and Orioles is a perfect example of this.