Yeah it's really cool how they could do that back then when the consoles weren't as powerful and they didn't have as much space on the disc to store the game data. CD-R were only 700mb and the special GD-Rom the Dreamcast used was 1gb. The dreamcast version only has Raymanian voices but that's likely due to the amount of space them much better textures would take up especially compared to the PS1 version. It's also running in 480i on PS2 and Dreamcast vs the PS1 240p also but I wouldn't take anything away from the PS1 game it's still brilliant
The PS2 has 4.7gb DVD and supports Dual Layer so they had all the space in the world for their resources however still limited by GPU/CPU power which likely explains Revolutions framerate but the graphics are unbelievable for a PS2 game.