Good lord, if you're gonna talk RPO's then know your stuff.
1) RPO's can be run from under center. The Packers were running basic RPO's in the 90's with Brett Favre under center. The backside WR would run a slant on certain run plays. If Favre saw the alignment he wanted then he had the ability to hit the quick slant on the backside. If the alignment wasn';t there then he'd give it to the back.
2) RPO's can have pre or post-snap reads. A pre-snap RPO looks at the number of hats in the box and the leverage the defense has. The QB makes the decision to give the ball or keep it and hit a quick pass based on the alignment here. This is what Favre and the Packers were doing in the 90's.
There are two other variants of RPO's that have post-snap reads. One version has the QB reading a backside backer or safety generally. He reads their movements and if they break on the give motion then he pulls the ball and hits the pass. If the key stays home then the QB gives the ball to the back. The other variant is basically what Auburn and Oregon were doing. It's more or less the triple option, but the pitch is replaced with a short pass, generally a screen or quick hitch. The backside DE is untouched. If he goes with the back then the QB keeps it and makes the decision based off of the defense to keep running it or to hit the quick hitter. If the DE does not bite on the back then generally the QB will give it, but if he does see they have leverage on the screen pass he can hit that, but the vast majority of the time it will be a give if the DE is staying home.