I shared your question with the SAP Ariba team that supports your company. I understand that the team delivered guidance on your questions. I'm sharing that guidance in this thread for the benefit of other community members.
In response to your first question, SAP Ariba OnDemand currently offers a report of active/pending approvers which can be manually run but does not include email information of the user. It can be scheduled to run automatically and a CSV or Excel version can be sent to an email address. We're looking into the possibility of adding WWID or an email address to the report but nothing is on our Roadmap currently.
Regarding your second question, we do have APIs on our roadmap in the 2016 timeframe that should address this requirement. We currently pass this information to our Mobile app.
SAP Ariba Exchange Community Manager