He is a SS.
They have "no depth" so you can expect him to play
I have no doubt he'll play but if their scheme is a "2 high" scheme, one in which the safeties both play deeper or are always on the same side of the field and rotate the "strong" safety responsibility based on the alignment of the offense, that will limit his opportunities a lot. IDP guys are looking for the old-fashioned pure SS guys, that are always lined up tight, involved in primary run support, and picking up either a TE or RB coverage responsibility. Those are the guys that rack up a ton of tackles. It's even ok/better if they aren't super athletic and/or are limited in deep coverage skills because that ensures they will be playing in tight (as long as they don't get removed from the field as a result). Kind of like I don't want my TE to be such a good blocker that they keep him in to block a lot (Witten) as long as it doesn't cost him targets for being so bad - Jimmy Graham and Antonio Gates being primary examples of what we want.
Landon Collins, Reshad Jones, Keanu Neal - these are the S studs. Byard put up huge numbers too but I didn't think he was the SS type and was completely unprepared for that, having him in no leagues, all the press I read and thought was that he was a FS type of guy.
The reasons I'm worried about Vaccarro are two-fold. One, Vrabel is the kind of stubborn-my-way-NEP-way-or-nothing guy that is likely to just play his scheme and if the guy doesn't fit it keep looking for someone that does. If that scheme is a 2 high scheme, it doesn't matter how good the guy is, it will ruin his (both S, actually) IDP value because it splits the tackle opportunities. The second concern is that Byard might actually be the better pure SS, so even
if they go more traditional, it might not even be Vaccarro that benefits. I didn't watch much Titans defense, but Byard's numbers were way, way out of whack with my expectations for him.