General supports external data. You can programatically update F0911Z1 with the journal entries and then run a batch processor to validate the transactions and create live transactions in F0911 and F0011.
See the Batch Journal Entry Processing chapter of the 8.10 General Accounting V2 guide for how to process the journal entries once they are in F0911Z1.
There are four separate date columns available (Century, Month, Day and Year) so you do not have to deal with Julian dates. Also, the F0911Z1 table only requires minimal information. For example, you enter BU.OBJ.SUB and the batch processor retrieves AID (short ID).
If your ADP data are in (or can be converted to) Excel, you can probably import into the F0911Z1 grid. See the heading Add a Batch Journal Entry.
Let me know how else I can help.