As pointed out by @hashar, we should deploy the ORES extension to the beta cluster before setting it up in production.
https://www.mediawiki.org/wiki/Writing_an_extension_for_deployment#Deploy_to_beta_cluster_on_Labs
AIUI, the ores.wmflabs.org service is based on data from production wikis, so if we wanted to truly set this up in beta cluster, we'd need to have an ORES instance that uses data from the beta wikis...and I don't know how difficult that will be.