Not at all, Quake 3's source code is GPL[1]. You can totally sell a game made with Quake 3's source, you just have to redistribute the source as mandated by the GPL. v{6}'s license is more restrictive.
The assets are a different problem. You can use the code without the assets and vice-versa.
The assets are a different problem. You can use the code without the assets and vice-versa.
[1] https://github.com/id-Software/Quake-III-Arena/blob/master/C...