I'm being a bit paranoid here, but the rebate form states that:
This promotion is valid only for purchases made at Beach Camera or beachcamera.com or buydig.com store or directly through such dealer’s own website. This promotion is NOT valid for purchases made through a marketplace, auction or other third-party website portal.
As far as I remember from my 50D purchase they send you a "normal" receipt that doesn't mention EBay. Does that sound accurate? Thank you!