The answer to be brief is: No. GD-ROM CDs can not be copied or written with normal CD burners.
as a GD-ROM can contain more information than a CD-R/RW (90 minutes instaed of 112+4 minutes). There are special writable CD-Rs; these however are only sold to official DreamCast developers and are not available to the general public. And anyway, a GD burner would be necessary.
The statement that the first DreamCast games could be copied may be correct but this was only possible because these games did not yet use the outer area with the high write density yet.
You can also forget the idea of writing DreamCast CDs on DVD-R/RWs as the DreamCast console can not read off of DVD-R/RWs.