Here is a question on StackOverflowa question on StackOverflow in which the poster discovers that a universal analytics snippet and an old style analytics snippet clash.
That person was able to solve their problem with a multiple tracker method:
ga('create', 'UA-00000000-0', {'name': 'myTracker'});
Even if those two didn't conflict now, they might start conflicting when Google migrates all accounts to universal analytics.