Howdy from Chattanooga (guessing from your workbook you're a fellow TN resident)!
I recently ran into a similar issue. The solution I ended up with was instead using the map to show the number of items present in the county, and having a separate worksheet that is filtered by a dashboard action that provides the details about each item present. So in your case, each county is shaded by the number of providers, and then you can click on a county (or multiple counties) to see the list of providers present in that county. I provided an example in the attached.
County Provider Map.twbx 306.1 KB
Attached is a workbook (version 10.1.5) illustrating a possible solution. This approach does 2 things: (1) compile a comma-separated list of provider names for a given county, and (2) lump multiple providers into a generic grouping for the legend.
This technique uses PREVIOUS_VALUE to compile a comma-separated list of all the providers for a given county. This is great for tooltips, but not for the legend — the names get so long that the legend cuts them off.
This technique detects whether a county has more than one provider, and if it does, it lumps it under "(# providers)". This makes for a clean legend, though you can't tell what specific providers cover a county without providing more detail e.g. in the tooltip.
Put 'Em Together…
By using Combined Name for the tooltip and Grouped Name for the legend, you end up with a pretty nice user experience.
Let me know if that's what you are looking for!
County Provider Map_JC-10.1.5.twbx 164.0 KB