Sure you cannot teach someone to be an entrepreneur, however there are many important disciplines you can gain from studying a business degree. Most executives hold an MBA - although this may be simply to speak-the-speak with others at that level.
Sheryl K. Sandberg (COO of Facebook) holds a MBA. Zuckerberg went to a world renown business school (albeit he dropped out).
Maybe you only need an MBA hire when you have gone public/IPO?