Not sure if this is what you are looking for, but yes you can read an XML file containing values and plot them onto the map. Using dojox.data.XmlStore function, you can fetch out the values in the xml file and as long as there is a latitude and longitude position stored in the xml, you can generate a marker for it. In the ArcGIS API for Javascript samples under Web Maps, there is a sample called Map with CSV data. The concept is the same, just using a CSV file for input vs. an XML file.