Using a different administration theme according to the role
The ThemeKey module lets you set the theme using many different tests. While it doesn't specifically set admin theme in the usual way, it will certainly let you set a theme for a role and a path, achieving the same result. Some more details about this module (from its project page):


  ThemeKey allows you to define simple or sophisticated theme-switching rules which allow automatic selection of a theme depending on current path, taxonomy terms, language, node-type, and many, many other properties. It can also be easily extended to support additional properties exposed by other modules