I have seen some mock drafts where Xavier McKinney and Grant Delpit fall to GB. They are clearly the BAP's. Can you justify not getting one of those guys?
With the Packers set at S with Amos and Savage, taking one of those guys requires a projection to the hybrid ILB position. While both these guys look to be strong safety types, they don't have the size for the ILB position as other than pass down rotational players.
While coverage ability at the the 3-down 3-4 ILB position is prioratized, there are too many tweener downs where that guy has to be able to diagonse and attack the hole, shed blocks, take on RBs with a head of steam.
Isaah Simmons, the most rounded player at the position in this draft with positional flexibility, won't drop anyhere near #30. He's kind of a beast. Murray has a high read-and-react quotient and is generally mocked higher than #30, but he looks more like a fit for a 4-3 zone-heavy D where he doesn't have to stray far from the line of scrimmage.
Patrick Queen would be the better option in this role than those safeties you named with better size at about 225 lbs. He's the best coverage ILB in this draft for the combination of zone and man ability. Now, Queen is not an all-tools player like Simmons nor does he have ideal length at 6'1" compared to Simmons' 6'4", though Queen is a better option than Simmons in zone coverages. Regardless, we don't have a top 15 pick to land a guy like Simmons.
What you would be buying with Queen is all-around coverage ability, safety speed going sideline-to-sideline, blitz ability, and a good fit for Pettine's man coverages. There isn't a lot to see from him in the way of read-react-attack or shed in the available tape. He was protected considerably by his D-line. However, you'd have to keep in mind he was a one year starter and judging from his zone reads in coverage I think you'd be getting a pretty smart player who should turn into a respectable even if not an exceptional run defender. You would need to pair him with a base run defense specialist, preferably a better option than Goodson, but those guys are not expensive. Ragland, to take one example, would be a good option as a pairing.
Compared to Martinez, whose read-react-attack and ability to shed blocks are all sub-par, you'd get an upgrade in the coverage ability alone.
There are good reasons you see Queen popping up in some mocks at #30. He's faster than Littleton, a guy in a similar mold, who won't cost the $10 million per year Littleton might command and he'd be a better option compared to Martinez who has been a jack of all trades and master of none regardless of whatever stupid money somebody throws at him.
I suspect Queen will test very high at the Combine. He may remain in reach because the league values length and he'll get dinged for the 6'1" height if that is in fact how he measures. If he bulks up to 230 and still runs like the wind, that might be a problem.
I can't say at this stage Queen would be my top pick, especially with all the unkowns, especially who is still on the board at #30, I would definitely put him on the possibilities list, and definitely above those true safeties you mentioned.