REST api for floating license server
One answer
Seeing that the License Server REST API Wiki has not been updated since 2010, and similar questions popped up every year in the past few years, I would say that such API is not available, yet.
https://jazz.net/wiki/bin/view/Main/FloatingLicenses
https://jazz.net/forum/questions/29444/is-there-a-rest-api-for-checking-licenses
https://jazz.net/forum/questions/58021/floating-license-rest-api
https://jazz.net/forum/questions/105790/what-is-the-floating-server-root-uri-to-use-the-licenses-rest-api
https://jazz.net/forum/questions/125310/how-to-get-user-license-info-via-oslc-rest-api