Here's the deal for the most part.
Rudi is in a contract year, they didnt resign him b/c they werent sure if he can handle the load for a full year, or if he can consistantly play at the level he showed flashes of last year.
The Bengals did believe enough in Rudi though to trade Dillon away, not knowing who they would have as his backup (shows confidence in him). Perry is a very quality RB who has the talent to start for this team in time. He will see action on 3rd downs and steal a few carries, but it wont be a 50/50 split.
If Rudi blows up and has a great year, you would think that the Bengals would resign him. But if thats also the case, he will be demanding a LOT of money. I dont think they can afford both him and Perry at RB. If Rudi has a bad year, he would be very cheap to sign, but Perry may end up beating him out
All that said, he looked very very good so far this preseason against some very good D's (NE and TB). He looks much quicker to the line then I remember, and was able to break through several tackles....He looked like the real deal.
I know that doesnt really solve anything, but it is a pretty complicated situation. He has the skills, but also has a 1st round pick looking over his shoulder. I do believe that he will be a starting RB in the NFL next year, I just dont know if it will be on the Bengals.