Nexus is a repository manager. It allows you to proxy, collect, and manage your dependencies so that you are not constantly juggling a collection of artifacts. In essence. it makes it easy to distribute your software.
The OpenShift templates are located in oc-config and can be compared with the OC cluster using tailor. For example, run cd oc-config && tailor status -l app=nexus3 -n cd to see if there is any drift between current and desired state.