It's awesome to hear that governments are trying out a non-MS OS for critical applications. In this case, the District of Columbia was trying out an online voting system. The server OS isn't specified however it's programmed with Ruby on Rails for a virtual Appache web server [1,pg18]. The crypto server is a modified (by RH) Fedora [1,pg17]. The bad news is that the UI was hacked and music was added to the process. The main article [2] doesn't say if the hole was linux related.
[1]
http://www.dcboee.us/dvm/DCdVBM-DesignRationale-v3.pdf
[2]
http://voices.washingtonpost.com/deb...nds_dc_on.html