SB Nation's Colts blog, Stampede Blue, weighed in recently with his chances.
Stampede Blue is a bit skeptical on Jackson, but as I did in that injury link, concludes he has a shot at making the team because of the instability in the secondary:
Regardless of how good of a player Jackson is, he's already in one of the best positions to make the roster among the group of undrafted free agents.
Jerraud Powers is really the only cornerback who is guaranteed a roster spot at this point. Between players like Kevin Thomas, Terrance Johnson, Chris Rucker and Cassius Vaughn, can anyone say with 100 percent certainty that any of them will make the roster?
I can't. And I can't think of another position with that much unpredictability.
Therefore, just by the nature of Jackson's position, he has a better chance of making the team than many of the undrafted free agents, even if I still don't expect him to contribute much as a cornerback if he does make it.
I'm not up on the Colts' situation enough and being so far away from the start of the season, it's nearly impossible to rate Jackson's chances at this point. But as Stampede Blue points out, he's got NFL size and that's a start. I also think his special teams abilities will help him and if he makes the roster, that will probably be at least part of the reason since he's not likely to step in right away and contribute heavily to the secondary.