So I'm in the process of getting a 18" 6.5 Grendel put together.  I've got a Dead Air Sandman K in ATF jail.  

Is there going to be a noticeable reduction in recoil with a muzzle brake compared to a flash hider with the suppressor installed?

i use f/h on my guns 16+ inches and brakes on ones less tha 16. i know brakes are louder but i rarely shoot with out a can, f/h dont need to be timed and on short barrels the brake acts like a blast baffle

Muzzle brake.

You have a suppressor, can use it when you don't want the flash/concussion, and it saves the blast baffle somewhat (more so with short guns/high firing schedule). For most users, however, the fear of blast baffle erosion is overblown.

More importantly, at least in some cases, the greater surface area the brake engages with the mount (in some manufacturers) the suppressor will be more repeatable/less POI shift.