Pentaho can get data via webservice but only via the ETL tool. So you'd still want to have it stored in a DB that pentaho can access somewhere. Although; If you really wanted to you can actually have a transformation that feeds directly into a report/dashboard. ( And results can be cached too if you want )
The pentaho dashboarding framework is very good, google around for "Ctools" from Webdetails it's got some great demo's to help you get started.