Please take a look at the Procurement Solutions Integration Guide for PeopleSoft that is available on iConnect. You should be able to find answers to most of your questions.
In short, yes this export is available on web service and we do suport Peoplesoft 9.0. But the web service integration with PeopleSoft does not have out-of-the-box end-to-end integration. You will have to develop the code to accept the SOAP message from Ariba and persist the data in the PeopleSoft tables.
Please take a lok at the guide if you haven't done that already and let us know if you have more questions.
P2P - Solution Manager, Ariba