Dont know if this is of any help……….Ive copied and pasted this reply to a query I had on the Vegas forum……..
Files created in PI need to be rendered. You can export a picture sequence (I use .PNG files for Vegas), with or without the background scene.
Turning off the BG in PI when rendering and saving the alpha channel gives greater flexibility of the PI element in post…you can further adjust transparency, etc. if that element is separate from the BG.