The zones are counties Jeff, and there isn't a state in the union with more counties than the maximum unique values to render so it should be building a table during the conversion. At this point, I would suggest Rob contact Esri Support and have an analyst go through it with him. Rob posted this same question to the GP forum but included more details in that thread, specifically about the background gp process failing with error messages. The first test is obviously running it in the foreground to narrow the issue down. After that, I would do what you suggested and convert the zones into raster datasets and run it again, to narrow down the issue some more. Support will know what to do in terms of other troubleshooting.
Best,
Eric