When deploying the FAH to PeopleSoft General Ledger integration, the aim should be to have external feeds to PeopleSoft General Ledger flow via FAH. If not then... there's no point in implementing FAH in the first place.
Just like implementing FAH against E-Business Suite General Ledger serves the purpose of having external feeds to E-Business Suite General Ledger flow via FAH.
There is one difference though:
When using E-Business Suite General Ledger, Subledger Accounting (SLA) connects the E-Business Suite subledgers with the E-Business Suite General Ledger. Hence (as explained in this post) all subledger data (both E-Business and non-E-Business) is flowing through the common XLA framework, towards E-Business Suite General Ledger (XLA = FAH/SLA):
But in the FAH + PeopleSoft General Ledger scenario, the PeopleSoft sub-ledgers continue feeding PeopleSoft General Ledger directly, without any FAH/SLA involvement what-so-ever:
Sure, you could connect the PeopleSoft sub-ledgers through FAH. That would definitely be an entertaining project. But from cost/benefit perspective it wouldn't make much sense.
So when using FAH in combination with PeopleSoft General Ledger, the integration between PeopleSoft sub-ledgers and PeopleSoft General Ledger remains untouched, and the PeopleSoft sub-ledgers continue feeding PeopleSoft General Ledger just like they've always been doing: without FAH.