On the VZ SV6 manifold just were the inlet is, there is a hose attached to the front left pipe on the manifold. What is that rubber hose actually for? If it is cracked does it matter?

I believe that that's part of the crankcase ventilation. The problem with it being cracked is not so much due to the crankcase ventilation, but the fact that it will cause a vacuum leak in the manifold. This results in a poor idle.