Dreamcast disks

Yes and no. If you mean with intentions to copy the game, then defnitely not. but on a gd-rom there is a small area that is readable by normal cd-rom drives, some games may have some extra features in that area (picures, some demo disks have sega swirl pc version, ect)
Ive also heard of at least one DC game having a screen saver on the track thats readable by computers. Unfortunatly, the game im thinking of was recalled because of the screen saver containing a virus. I can't remember the name of the game though...