What is the purpose of monitoring rancher? If it is written in Java or .NET it will be possible. But in general in such cases most of the time it will be fine for you just monitoring it as a process. Transactional monitoring doesn’t have sense because you have really limited option for impacting how it is handling transactions. So in general you will not use it. Better approach I think it would be monitoring it as a process with some extra metrics fetched from it via plugin (if rancher is exposing them somehow).
Containers orkiestrated by rancher will be monitored the same way as any other containers.