The link from CU Resources only allows access to the production environment. You can still access the Reporting environments through the planets page.
There is a system-status section for each system on the right column on the news page. This will tell you if any of the systems are currently down.
Exception: When the HRMS is down for monthly processing, the link in CU Resources will still take you into Production HRMS, but in view only mode. You can still run reports and queries on these days, only no data entry will be allowed.