My understanding is that the Reds have not COMMITTED to a three man rotation. They have left open the possibility of Homer starting game 4, although maybe not.
I'm guessing that if the Reds are up in the series 2-1 Homer will get the start. If the Reds are trailing then Cueto will start game 4.
In addition, Lecure, Marshall, Brox, and Chapman all pitched last night. Homer will go five tonight and the other guys, Arredondo, Simon, Hoover, whomever, maybe even Leake, will get a little work.