Wow, I get busy for a week and I miss a critical thread (to me anyway)!
SIMP is absolutely complimentary to the SSG and to OpenSCAP. The SSG is part of the policy/guidance stack upon which SIMP is based. The goal of SIMP is to be able to ramp teams up to the 80% mark in terms of both functionality and compliance that pretty much all teams require.
Instead of being rigid, we are attempting to allow for maximum operational flexibility so that 1) you understand what you've got on your systems 2) you understand *exactly* what you've changed over time, and 3) you can make minute changes to systems based on operational requirements and repeat the whole deal consistently across different environments.
We've had a bumpy ride transitioning to working with the standard Internet stack but we've gotten to the point where others should be able to successfully build the SIMP installation stack.