What are the supported Operating Systems for License Servers?
For example, can Solaris OS be used as a Server?
Also what versions can be used?
Xilinx supports the same Operating System versions for License servers as are supported by Flexnet.
The list of supported operating systems for licensing can be found at http://www.flexerasoftware.com/support/additional-support/end-of-life/flexnet-publisher.html
More details on the list of supported operating systems can be found in each FlexNet Publisher Release Notes. For example, see FlexNet Publisher 188.8.131.52
To obtain License utilities for Windows, Solaris and Linux see (Xilinx Answer 33022)