When exporting a movie file from Titler Pro, the exported MOV file includes an alpha channel. You may need to adjust your NLE to make sure that it sees the alpha channel. For example, in Vegas, you would right-click the event and choose Properties. On the dialog that opens, go to the Media tab and change the "Alpha Channel" setting to the proper setting. Straight, Premultiplied and Premultiplied Dirty will all work fine.
Note: The file format that Titler Pro uses for movie exports has been deprecated and is no longer supported by most NLEs. We are working to change it to a more modern format.