Figured it out myself. I was missing a autocomplete flag. Silly mistake but it's all good now.
var geocoder = new Geocoder({
arcgisGeocoder: false,
geocoders: [ {
url: "http://maps.hrsa.gov/arcgis/rest/services/Locators/HDWSMPComposite/GeocodeServer",
name: "HDW",
placeholder: "Find a place",
outFields: "Xmin, Xmax, Ymin, Ymax",
singleLineFieldName: "SingleLine"
}],
autoComplete: true,
map: map
}, dom.byId("search"));