I can speak from experience. My brilliant school cut internet access in all student housing in mid August; I refused to take boards without having access to practice questions. I did not find myself in non-school housing until after October 15, so I ended up taking Step 2 CK late (in December).
Basically, they hound you for your scores for a few days/weeks. Eventually, you get put on involuntary leave of absence. Your stipend and benefits are suspended and reinstated retroactively once the office receives a passing score. I *think* if you get put on LOA because of noncompliance and do not provide a PASSING score by whatever deadline they choose, you may lose eligibility for the scholarship, meaning you only get one shot to pass. This may or may not be true, I don't know -- thankfully I passed on the first try and did not have to find out.
I still matched and all without having any Step 2 CK scores. However, I was not applying to a competitive specialty so I don't know if it would matter in something more competitive; I think it might.
As far as the CS, I think the Army is like most people -- they don't really care about it. Just pass.