Andrea Veri commented on a discussion:
Exactly, you could theoretically have a BuildConfig that has a Dockerfile having a FROM field pointing to GitLab's internal registry instead of default docker.io. As an example:
FROM registry.gitlab.gnome.org/namespace/imagename:tag
You will also need a build pull secret in order to successfully fetch the image, documentation is available at https://access.redhat.com/documentation/en-us/openshift_container_platform/3.11/html/developer_guide/builds.
Please keep in mind that any image based on top of the aforementioned distributions will fail to run on the cluster (due to the clone3 syscall invoked whenever a child process is created).