I do this quite often and it's usually successful. Not all RPs, but a lot of them. You might need 4 starters depending on the league settings. Like I said, you still have to reach the IP maximum in order to be competitive. Instead of having a bunch of hitters on my bench that I never use, I load up on RPs. I guess my situation is different because my main league has 8 bench slots which is a lot. And this is roto. Take a small hit in Ws but have a big step up in SV, ERA, WHIP and Ks. It's going pretty much according to plan, as my hitting is dominating and I'm near the top in every pitching category except Ws (Cliff Lee is partially to blame for that, too) and overall I have an 11 point lead over 2nd place.