Thanks to Andries Smit a version for Mendix 5 is submitted to the appstore.
The quick fix to get it working is to remove the AMD loading of dropzone and just expose the "Dropzone" via global scope.
//if (typeof exports == "object") {
// module.exports = require("dropzone");
//} else if (typeof define == "function" && define.amd) {
// define(function(){ return require("dropzone"); });
//} else {
this["Dropzone"] = require("dropzone");
//}
})();