Nathan,
So you are using
var markerSymbol = new esri.symbol.SimpleMarkerSymbol(esri.symbol.SimpleMarkerSymbol.STYLE_SQUARE, 28, new esri.symbol.SimpleLineSymbol(esri.symbol.SimpleLineSymbol.STYLE_SOLID, new dojo.Color([27, 236, 86]), 0.75), new dojo.Color([255, 0, 0, 0.30]));
and the correct object name is esri.symbols.SimpleMarkerSymbol
var markerSymbol = new esri.symbols.SimpleMarkerSymbol(esri.symbol.SimpleMarkerSymbol.STYLE_SQUARE, 28, new esri.symbol.SimpleLineSymbol(esri.symbol.SimpleLineSymbol.STYLE_SOLID, new dojo.Color([27, 236, 86]), 0.75), new dojo.Color([255, 0, 0, 0.30]));