This should be compatible.
MPN: SORJ72001 includes the Sig Sauer MSR red dot and Juliet3 Micro magnifier.
Yes, the SIG SAUER Romeo-MSR 1x20mm Compact Red Dot/3x22mm Micro Magnifier Combo Kit will be compatible with your NAK-9 and fit to the flattop picatinny rail.
The SIG SAUER Romeo-MSR 1x20mm Compact Red Dot uses the Aimpoint T1 footprint. So any lower 1/3 co-witness mount for the Aimpoint T1 will work with the SIG SAUER Romeo-MSR 1x20mm Compact Red Dot. The Juliet3 Micro Magnifier has spacers available for purchase to allow you to raise it to the height of the red dot. The Midwest Industries Aimpoint T-1 QD Mount at the link below will work with the SIG SAUER Romeo-MSR 1x20mm Compact Red Dot to achieve 1/3 co witness. The spacers for the Juliet magnifier can be purchased through Sig Sauer.
https://www.opticsplanet.com/midwest-industries-aimpoint-t-1-lower-1-3-qd-mount.html?_iv_code=MWI-RMT-ATQDM-MI-QDT1-1-3&_iv_attachment-mount-type-1726386052=1-sl-3-co-witness-mount
Yes this can
You will have to use a lower 1/3 mount.
The Sig Sauer ROMEO-MSR 1x20mm Compact Red Dot is a durable sight and will hold up through natural use but its hard to say how hard you would have to hit it for it to lose zero. I recommend if you hit it on something pretty hard, you should confirm zero just to be safe.
I would assume so as in the Sig MSR Red Dot was rated for rifle cartridges shotguns and something else so I'm pretty sure it would be able to handle a 300 blackout.
The red dot is only set at 1.41" height and the Juliet3 Micro magnifier can be set at 3 different heights (1.41", 1.53", 1.63").
Yes, the Sig MSR red dot is at an absolute co-witness height so backup irons will be visible through the red dot window.