Interestingly, for a long time there were no publicly available tools for or docs on dumping GD-ROMs. New releases from Echelon and Kalisto would appear promptly, so there was obviously a way, but you could only partake in the rampant piracy by downloading the (occasionally-massaged to fit on a CD) disc images online.
A lot of discussion in the (tbf probably quite young and inexperienced) community was around how this was possible. A popular theory/rumor at the time was that they were using CD drives with modified firmware, for example.
This probably also helped keep the piracy amd homebrew scenes fairly well separated on the Dreamcast, as there was a lot of info and examples around running your own code. This is in contrast to eg. the Xbox scene, which was in many ways the equally vibrant successor to the DC scene, but where piracy and homebrew seemed much more intertwined. Not least because all the homebrew binaries were built using the off-limits Microsoft SDK, so you had to go to some shady FTP site via links found on IRC to download them.
There was even a preview version of the game I worked on that got leaked so either someone in our office was part of the cracking scene or someone at Sega/QA (they were our publisher) since AFAIK no-one else had any copies.