It is not clear which part of the license system handles the end user license and which part handles the demo license.
Having both TAC Vista and SmartStruxure installed on the same PC can cause conflicts in the license system.
TAC Vista, SmartStruxure Solution
If a SmartStruxure installation is only used for engineering and therefore will only have demo licenses activated, you don't need to install the license server. The service "FLEXnet Licensing Service" is installed by any SmartStruxure software package, and that is the service that will handle the activation of demo licenses.
If you will only use demo licenses on a PC and/or also have TAC Vista installed on the same PC, only install the license administrator and not the license server.