If it is a web front-end you should be able to monitor it. We run Confluence in our company and we monitor it fine with an HTTP/HTTPS monitor.
Are you looking to monitor Atlassian's page that you noted or your instance of Confluence?
If it is your company's instance, you may need to use the on-premise poller system if it is only accessible from inside the company's network. www.site24x7.com/help/getting-started/on-premise-poller.html