There are no difference between RedHat OpenStack and OpenStack. Let's discuss one by one.
OpenStack is a set of software tools for building and managing cloud computing platforms for both private cloud and public cloud. Companies uses this for making there own private cloud. We can know how cloud works internally, if we go for OpenStack.
RedHat OpenStack is a commercially supported distribution of open source OpenStcak software designed to build and manage compute, storage, networking resources in private and public clouds. RedHat offers OpenStack certification program.
Hope it will clear your doubt.