Last season, Santana hit right handed pitching at exactly MLB average (100 OPS+). He's not helpless against right handers, but he isn't an asset (according to last year) and his platoon splits are far less pronounced than the three lefties (Kirilloff, Wallner, Julien) last year.
A lot of good switch hitters have their platoon split vary from year to year, others are always better on one side. Polanco had been consistently better against RH pitching until last year, when in a half season, he put up his best OPS+ versus lefties. Until proven otherwise, I would expect Lee to be marginally better against righties, but not a true platoon candidate.