If it is not on the Current Isilon Software Release document that you linked, it is not available just yet. I also verified there is no documentation available at this time for OneFSv8.1.1.
Right now 8.1.0 is the latest GA release (General Availability) and 220.127.116.11 is the latest Target Release. The document explains the difference:
A OneFS release is designated as Target Code after it satisfies specific criteria, which
includes production time in the field, deployments across all supported node
platforms, and other quality metrics. To ensure that your clusters are running the most
stable and reliable version of OneFS, upgrade to the latest Target Code available for
the OneFS family that meets your business needs.
Target Code represents minimum OneFS release recommendations and does not take
into account unique storage workflows. When considering which version of OneFS to
adopt, be sure to review your business needs with your EMC Isilon account
representative. You may also want to install a later version of OneFS to take
advantage of new or improved functionality.