Currently the installer expects to get a vip-dns parameter, and also runs verification on its validity and will fail installation in case of miss configuration. On the other hand, the system itself ignores it - keepalived will not be using it and the openshift cluster does not rely on it. So, currently, its just add more requirements on the end user. Also, it affects the assisted installation workflow.
*** This bug has been marked as a duplicate of bug 1840496 ***