Hernandez is expected to miss between 6-8 weeks, having broken the hamate bone in his hand during Tuesday's game against Oakland. It appears he may have injured it on a swing, which seems kinda odd, but the bottom line is, surgery is now required, and Hernandez will start the season on the DL. That does not affect his status as a Rule 5 pick: whenever he returns, Oscar will still need to be placed on the 25-man roster, or returned to his original club. [Though, as GuruB dug out, a Rule 5 pick needs to spend at least 90 days on the active roster in that first season; if he doesn't, the balance is carried forward to next year]
So what of the other seven catchers in camp?
Tier 1: Peter O'Brien
He still seems to be ahead of the pack at this point, with the job as starting catcher apparently his to lose. That will depend largely on his defense, which O'Brien has been working on at Salt River Fields since the first week of January. Colleague Archie Bradley has seen advances and the effort the catcher has put in: "I think the thing that needs to be said the most about him is his work ethic. The improvements he's made catching, throwing guys out, his footwork, everything [is better]. He's obviously a very gifted athlete, but to see him put in the work and to see the improvements he's made, it doesn't surprise me at all. He's improved a lot."
Tier 2: Gerald Laird and Tuffy Gosewisch
They would appear to be front-runners for the backup job, and it's hard to separate them. Both are defense-first catchers, which would make sense given O'Brien's offensive inclinations. Laird has the advantage of more major-league experience, but the well-liked Gosewisch was with the team, as Miguel Montero's backup, all last season, and so may be more familiar with the pitching staff. How Laird would hold up is an issue: he hasn't had 200 PAs in a season since 2010. Chip Hale said "We know what Gerald can do. We just need to make sure that he's ready. If and when he makes the team, he'll have to catch. How much can he catch for us? We'll have to figure that out."
Tier 3: The field
The other four catchers in camp are Jordan Pacheco, Blake Lalli , Matt Pagnozzi and Mark Thomas, and would still look like outsiders in this race today. Pacheco is probably ahead of the other three. While he may end up making the Opening Day roster, that's likely due to his ability to play other positions; Pacheco has not put on the mask for us, since Arizona picked him up off waivers from the Rockies in June. Lalli does have a smidge of major-league time (40 PA with the Cubs and Brewers in 2012-13), while Pagnozzi has slightly more (105 PA, from 2009 through 2014). Both would seem more likely candidates for Reno, along with the loser of the back-up spot.