I normally "scuff up" the aluminum with a Dremel so that the Marine-Tex has something to hold on to.

A skim coat can't hurt, although one of my most accurate rifles, a M700 VS in 22-250, easily shoots under 1/2 MOA regularly, and has had nothing done to it bedding-wise. (I'm actually scared to touch it )

do stocks with bedding blocks or pillar beds (HS, mcmillian, hogue, etc) need to be glass bedded?

Yes. They still need a skim of bedding to insure they`re right.

so do i need to relieve some material or just "fill in the cracks"?