Turns out its not angularJs (although angular is big enough that I could see that being a red herring). Turns out it's the presence of a now function on the Date prototype (in my case, added by the dateJs library).
TweenMax.js (at 5701) has the following declarations (emphasis mine):
var _reqAnimFrame = window.requestAnimationFrame,
_cancelAnimFrame = window.cancelAnimationFrame,
_getTime = Date.now || function() {return new Date().getTime();},
_lastUpdate = _getTime();
Because dateJs adds a now method, _getTime is set to an existing function (one that returns today's date/time) instead of the IE9+ function that returns the whole milisecond data gs is expecting. Not sure why that line looks for now first (instead of just setting _getTime to a function), but the following change seems to work in all the browsers I have access to on a sunday afternoon.
_getTime = function() {return new Date().getTime();},
I can adjust to fix, but thought you'd want to take a look and decide if it's worth adjusting in the library(thought i'd pass it along just in case). Also - ThrowProps+dateJs = fail without that little adjust (in case anyone else is curious).