Same issue here. Latest version of DOM and Uploadify (from github).
Using an Uploadify-Field in a Page or DOM-Poupup (eg. by editing an existing entry) works fine, just not when using the "Add NameOfDataObject" button with the ImageDataObjectManager.
I'm sure it worked a few versions back..
Update: Upload doesn't work in the "Files & Images" tab either. So it's most likely a bug in the DOM and not in the Uploadify code. I'm not able to track it down though. Got no error in the logs.. the upload just keeps sitting at 0%