Yes and no. While I'm sure a muzzle brake on a 20" heavy barrel .308 does reduce felt recoil, it can also dramatically increase both felt and heard muzzle blast to both you and anyone around you.
I have a 20" heavy barrel .308 (Ruger Hawkeye Tactical) and honestly see no need to have a muzzle break on it to reduce what little recoil there is after the weight of the rifle, scope, bipod, ammo (over 10lbs. at this point) and the recoil pad take the oomph out out it.
I do admit that everyone's level of tolerance is different however.
Personally I would look at it this way, if it comes with a muzzle brake, and you don't like it, then at least you still have a threaded barrel to hang whatever else you want off of it, either a flash hider, a suppressor, both a flash hider with a suppressor on it (same with a muzzle break depending on types for everything involved) or even just a thread protector.
Unless you'd rather have a completely 'clean' barrel.