No, Doom's source license is GNU Public License. It's F/OSS. Its assets remain proprietary, but not all of them are paywalled, due to the shareware releases which include plenty of levels.

I believe the implication of OP's comment is that Doom and Wolfenstein 3D were originally released under non-commercial source available licenses before being relicensed to a FOSS license (GPLv2) a few years later, and the same could very well end up happening for Rogue Legacy as well.