Nagendar,
You might require PSINDS on Gateway server as well. I do not think these Fiori apps are designed in a standard way. There is not much documentation about these Fiori apps as well.
For example there are many SAP Notes (ex: 2110637) related to "FLM Fiori". Many of them contain both UI Fixes as well as Gateway fixes. That means that they have considered only embedded deployment. So you might end-up installing PSONDS in Gateway as well, and install all bug fixing notes in both Gateway and Backend.