On one hand, the Princeton - Wisconsin weekend is pretty clearly the second half of a 'home and home' series; Princeton at UW last year, UW at Princeton this year. And UW going all the way to NY to play a brand new team (the rest of whose schedule is St Anselm and Franklin Pierce) seems awfully unlikely; I'd find it slightly more believable if is were LUI coming to Madison.
On the other hand, for some reason and oddly, the UW schedule has been posted at their web site for about a month now, but never officially 'announced'.
I googled the LIU coach to see if somehow Coach Johnson or AD Barry Alvarez know him, are friends with him, etc etc, and would be willing to do him a favor (UW football contracted with UNLV to play in Nevada years ago largely because an assistant AD at UNLV used to work for UW). The only thing at all close I saw was the LIU coach used to be the head coach at St Norbert's College, a DIII program in De Pere, WI (just outside of Green Bay).
In short, I'll believe it when UW says it is happening.