Using Drupal Views and the contributed module CiviCRM Contact Distance Search I was able to create a search tool to enable unauthenticated users to find contacts and show them on a map based on proximity to a target location, and also via other exposed parameters. Drupal Views enabled me to show a name and some other data from the individual contact record and address data and org name from related org records.
The built-in proximity search function looks to be based on a profile and so won't let me mix fields from different record types.
Now I need to find a solution, or a developer who can build a solution, with Wordpress as the CMS. Has anyone created anything like this?