None of the backups are proven and there is an easy argument to be made that neither are Bonner and Jarrett.
This August will be about solidifying the starting roles while finding some talent to rely on in the second unit. However, Gray could prepare in August for a number of strategies that could happen this fall.
This is why it is so crucial for Aromire, a sophomore, and Cole, a redshirt freshman, to have a really good first few weeks of camp. If they do and either Jarrett or Bonner goes down, the easiest thing would be to just plug in a reliable backup.
In addition, given the relative inexperience of both of the starters, both Aromire and Cole could easily compete for significant game opportunities. Rover is really the only position where that could be possible and Gray has done that in the past, splitting time between Dorian Porch and Davon Morgan a few years back.
Exum has played extensively at both rover and free safety to date in his Virginia Tech career, so a quick slide back to either position likely wouldn't be too problematic for him. However, it could create a gaping hole at cornerback if Manning or one of the incoming true freshmen does not emerge as a reliable option.
Fuller is the kind of player that could play anywhere and be effective. He'd probably be a good mike linebacker if given the shot. His natural instincts and fundamentals are off the charts, and that's before you add in some very good athleticism.
A move to safety is far more realistic than one to linebacker though and it would be a fairly easy one for the ultra-talented Fuller. He's got good size and ball skills and given the fact that he has played a major role in each of the past two seasons, there's no doubt he call out signals defensively for the Hokies. However, this is probably a distant third behind the first two options to solve in injury problems at safety.
Right now, the only known backup is true freshman Manning, who enrolled in the fall. Beyond that, who knows who will take plays this fall.
Depending on how well Aromire or Cole perform in August, this could vault ahead of Plan A quickly. Gray will have to judge this on if he trusts Aromire/Cole more than he trusts Manning/Tookes. If he trusts either of the backup safeties more than the backup corners, then moving Bonner or Jarrett back to corner in the event of an injury would make sense. Both played a decent amount at corner in 2011 and would be able to pick up the position quickly one more.
Exum is entering just his first year at cornerback and, despite the high expectations for him given his spring performance; there is still a chance he struggles week-to-week in 2012. If that happens, then the quickest solution would be to swap him back with either Jarrett or Bonner and return Exum to a position he played a lot at in 2010 and 2011.
I'd put the chances of this happening at less than 1% given not only Exum's talent, but also his experience and versatility. He's had a large role in each of the past two defenses so the chances of him suddenly being not good enough to even be a major factor are remote.
See Plan A from the "Inconsistency/Weak Play from Exum"
A demotion would be far more likely in the case of Jarrett or Bonner than in any situation with Exum. Jarrett and Bonner haven't proven anything at the ACC level and are entering 2012 looking to prove themselves.
If it so happens that they need a little bit more development and Gray doesn't want to move Exum or even Fuller from either cornerback spot, then it would be the next best move to simply call up Aromire or Cole to the big time.
Gray already has both practice at each position, although it is widely expected that Jarrett will see the vast majority of his playing time at free safety and Bonner the vast majority at rover.
However, if they struggle in either position, it might make sense to just swap them to see how if it can give either a little bit of a jolt to play better. However, this is probably the least likely of any contingency plans for this issue.
Gray obviously has a lot of talent, a lot of versatility, but also a lot of questions to answer this August. He needs repeat production from each of his starters (excluding Fuller) and strong play from four guys to fill in his top backup spots. No matter what, Gray is going to have a lot to determine throughout the first few weeks of August so expect to hear about even more experimentation in the secondary as camp begins.