Yes, output parameters are accessible in attributesStack property, which contains attributes + inputs + outputs.
Some sample code showing to iterate over them:
var attStack = workflow.attributesStack;
for (var i in attStack) { var elem = attStack[i]; for (var j in elem) { var att = elem[j]; System.log(" name " + att.name); System.log(" type " + att.type); System.log(" value " + att.value); }
}