I'm not sure if this is exactly what you're looking for but Bullhorn has Google Maps integrated w/ their ATS so if you have a candidate/contact in your database it will show you where on the map they are. Akken's staffing software will be integrating that in the future too.
Several vendors offer the Google Maps integration (us included, however we require that the end-user customer become a Google customer to use it, at least at the moment), and the Google geo API does do exactly as you describe- takes a dataset and pins them all to one map view. If you would like to see that in action, pls ping me via RBC email.
However, all your current ATS offers an easy export of the dataset, then you have all kinds of choices for geospatial display.
You might find this organization useful as they offer a lot of interesting value-adds beyond just the geo info (i.e. demographics)