SlideShowpro Director 1.4.1 has been released and has watermarking:

Director 1.4.1 includes new support for built-in watermarking, allowing you to upload an image (transparent PNGs work best) to use as a watermark, then Director composites that image on your original content when it creates the optimized copy for your slideshows. You can define as many different watermarks as you like, and change what watermark is applied on a per-album basis. You can also control the positioning of the watermark and its opacity when composited with the image.

Now all I want is that it doesn't strip metadata (there's a hack).