Federal HR used to be its own module and I'm not sure that it still is. Federal requriements for reporting, pensions, taxes, payroll, were are pretty specific and dissimilar enough from the regular HR module that they made it it's own. I believe the new(er) versions of PeopleSoft didn't differentiate the two but there are different pages used and differnt flags are set based on the installation table. I would never assume anything and ask specific questions, such as, name five things that are unique about a Ferderal employee versus a non-federal employee and see what they say.
Federal HR is a part of the PeopleSoft HR application. Its designed specifically to suit the requirements of US Federal Government, any Legislative Changes in this application are governed by OPM (Office of Personnel Management - USA), EHRI (Enterprise Human Resources Integration) and such Federal Organisations.