Aperture is _terrific_ as a back-end store and catalog of an artist's works. I think you'll be pleased.
Note that you can add a watermark to your exports, and that this information is part of the Image Export Pre-set. Watermarking in Aperture is still a bit clunky, though. Once you are familiar with Aperture, you will want to get the BorderFX plug-in (and send some beer money to the programmer). This gives you extensive options for adding borders and text and watermarks to your exports. It becomes, in effect, a family of "Image Export Pre-sets".
Note, too, that there is usually no reason to save the "Web-ready" files in Aperture. You can always re-make them. Aperture functions as a conduit for making fully-adjusted image files from digital camera data files. Once you make the share-able image files to the specifications the recipient needs, you should send them along and delete them.