Three displays with Mac Mini 2012
Three displays will not work in a supported, OS X only solution. You can use two thunderbolt attached displays or one HDMI and one thunderbolt. 

Apple maintains a knowledge base article listing which Mac models support either one or two external thunderbolt displays.


http://support.apple.com/kb/HT4885


In the section for OS X, the 2012 mini is listed in the category of two full monitors with a footnote explaining HDMI and thunderbolt.