OpenStack is not listed under supported node drivers in the Rancher support matrix. What this means is that currently the OpenStack node driver is not officially supported and because of this, there isn't a supported way to use Rancher as the cluster self-provisioning platform on an OpenStack-based infrastructure.
This is not to say that clusters cannot be run in a Rancher-supported way on OpenStack-based infrastructure. To do that, the option of custom clusters will need to be used.
In the event of a Customer encountering an issue in such custom clusters, Rancher Support will troubleshoot up to the point of root-causing the issue. Issues root-caused to be in the OpenStack platform will need to be taken up by the Customer with the maintainer and provider of support for the OpenStack platform.
Also, troubleshooting by Rancher Support is currently limited to log analysis and screen share sessions with the Customer and does not extend to an OpenStack setup by Rancher Support to recreate the issue.