We have run into this when building RPMs for EL6. We are in the process of updating dependencies but until that’s done your going to have to update your SCL repo file to point to archived versions of SCL. Change /etc/yum.repos.d/CentOS-SCLo-scl-rh.repo to have baseurl=http://vault.centos.org/6.8/sclo/x86_64/rh/ for the repo centos-sclo-rh. Once that’s done do “yum clean all” and try and install ondemand again.