To be completely confusing, the Tags in the current vSphere API are not the same Tags as seen in the vSphere Web Client. Unfortunately, the Web Client Tags are actually stored and managed by the Inventory Service, separate from the vSphere API (and database).
Currently the only official version for managing the vSphere Web Client Tags is PowerCLI.
I did poke around with some SSL packet captures and it possible to expose those calls to other API kits (such as Java, Perl, C#, etc). However, I have not had the cycles to really build anything out. It was a mix of SOAP and some XPATH queries.