Re: Billy Hamilton continuing to excel at AA
IIRC, someone doesn't have to be removed from the 25 man per say. For instance, lets say on Aug. 30th, they decide Rolen needs to be shut down to rest up his shoulder again, so he goes on the 15 day DL. Hamilton (or anyone) comes up to replace him. When Rolen is off the DL, both players are eligible for the playoff roster. I believe the Reds used that loophole to allow some reliever on the playoff roster in 2010.
As for #2, while there is some risk there, I don't think its huge in terms of screwing up his development. You bring him up primarily to pinch run. If/when you clinch a playoff spot and your seeding, perhaps you give him a start or 2 down the stretch. Perhaps in a blow out he's given an at bat or two prior to that, but primarily he's used to pinch run, so I don't think you're going to screw up his confidence to much as he won't have much time to struggle at the plate. Now, since he's not being optioned back to the minors this season, he retains all 3 options. He goes back to AA or AAA to start next year, and has all season to develop down there. He gets 2 more complete seasons to develop in the minors or shuffle back and forth b/w cincy in the minors. In 2015, at the age of 25(?) he has to stick in the majors or pass thru waivers. If he's not ready to stick in the majors by the age of 25 he's likely not the superstar some hope he can be. If he's not on the 25 man roster by Aug 31st, then I see no reason to call him up in september. His speed could make the difference in a game or 2 in october, but I see no reason to start the clock if they don't put that option on the table.
A month of service time, probably isn't a big deal either as I'll assume he starts out next season in AA or AAA for at least a couple of months to get past super 2 status if he's ready to prime time action as early as next year.