"Does your Radius search plugin (application) work with the SobiPro import feature? Does it automatically geocode each listing by zip code. I have 4,000 entries and it would not be practical to geocode each one individually. Can you give me details on how it works?"
As I know, the Import application of Sobipro club, do not import any coordinates(latitude and longitude). Even if you have 2 columns for lat/long, the Import app is not able to save the coordinates, this because the coordinates are saved in special fields (compatible with Sobipro Geo-plugin).
Our Myjoom Radius search application work with the coordinates of the entries. But this application never change the coordinates of the entries.
So in summary you need to have your entries geocoded (having coordinates (lat/lng)) to work with the Radius search application. See this how to Geocode Sobipro entries article.
Also, with Geocode Factory, we provide a tool to display the Sobipro search results on a map.