Without wishing to go off at a tangent into receommending other products... I can answer your question directly and say, "yes, I have experience of Inbound Manufacturing Processors". We used these extensively for Inbound and Outbound to communicate with Shop Floor Data Capture systems. This was with OneWorld Xe and I made some notes that I can dig out for you if you are interested.
I recall that we didn't use flat file communication. Instead we just mirrored the data in one Oracle database to the JDE one. We would run a small executable every hour to copy the data over to JDE. Then the Processor can be run in Scheduler.
We had very bad problems with the Superbackflush processor which had some, err, features. But the rest were OK.
One of our sites used Z-Files in conjunction with API's borrowed from the Bar Coding interface project. This enabled us to use the MBF's to import the SFDC data, process it and then reject the problem data into the F31122Z1 where it could be manually processed.
I have not used these Processors with PLC's. Your problems might be different from the sort of user-mistakes we experienced if your data is machine-generated. However, all I can say is that the Z-File processing in OneWorld is a godsend and has made data conversion and some interfaces a real pleasure to put together.