Yes, the Primary Arms OpticsPlanet Exclusive 5x36 Gen III Compact Prism Scope actually includes a low mount with a spacer to put the centerline at 1.41" for AR platform rifles. However, the low mount will put the optic as low as possible making it ideal for AK's, Bolt Guns and more. You can also use aftermarket mounts designed to fit full sized 3x Power ACOG scopes, such as the TA01, TA11 and TA31.
The Primary Arms OpticsPlanet Exclusive 5x36 Gen III Compact Prism Scope uses a spacer that sets the centerline height at absolute co-witness (1.2"). Meaning the reticle will be exactly in line with your front sight post. However, because it is a 5x prism, the front sight post will be blurred in the optic window.
The Primary Arms OpticsPlanet Exclusive 5x36 Gen III Compact Prism Scope uses the ACSS AURORA Reticle which is specifically designed for 5.56 loads. It can work with 300 Blackout, but the holds will be different from the 5.56 holds on the reticle.
You will want a 7.62x39/300 BO reticle optic instead for proper BDC.
Yes, believe it or not by the ballistic trajectory for 556 and 762 NATO are robustly similar out to 300 yards, where the differences really start to widen passed 1" delta. Obviously your mileage will vary based on specific bullet weight, coefficient, and velocity compared to the 556 NATO standard used to mark the hatches. Check you local ballistics calculator to see for yourself how your 308 compares.
The Primary Arms OpticsPlanet Exclusive 5x36 Gen III Compact Prism Scope has an etched reticle which can be used if the battery dies.