Here's info we got from ESRI when we asked about this:
A potential workaround is to update the tile urls after the layer is loaded and replace http with https, here's a code snippet that shows this.
function init() {
var map = new esri.Map("map");
//Creates the Virtual Earth layer to add to the map
veTileLayer = new esri.virtualearth.VETiledLayer({
bingMapsKey: '', //set to your key
mapStyle: esri.virtualearth.VETiledLayer.MAP_STYLE_AERIAL
});
dojo.connect(veTileLayer, "onLoad", function(){
veTileLayer.tileServers = dojo.map(veTileLayer.tileServers, function(tileServer) {
return tileServer.replace("http:","https:");
});
map.addLayer(veTileLayer);
});
}