Employers know what DEFCON is, and there is nothing formal about any training received there.
The topics are invaluable, the experience gained there can beneficial, and the social networking has potential. However the bottom line is that DEFCON is not formal training by any means. You can not cram the value and complexity of a properly planned conference, into just one of the 45 minute talks presented there. Also, at official business conferences you do not have laptops and ATM machines coated in imagery that makes hardcore pornography look like G rated material, and people drinking vodka from plastic bottles from dawn to dawn.
I enjoy a trip to DEFCON. However I would never expect my employer to pay. You might as well ask them to pay to send you to Comic Con.