The HOMEPAGE is just some forum that links to a Wiki which is down. I can't find any information, so I assume all-rights-reserved is correct.
It is hosted at SourceForge, though: http://sourceforge.net/projects/deng/files/Resources/jDoom/ I wonder how this goes together with the SF terms of use, which generally require OSI compliant licensing.
From jdrp.box/info in the 20070404 version: version: N/A summary: 3D models and special effects for jDoom contact: danij@dengine.net author: Daniel Swanson et al. Packed by Harry 04/04/2007 copyright: Copyright (c) 2007 Daniel Swanson license: Free for non-commercial use readme = "The jDoom Resource Pack represents many years' worth of work. Several people have contributed 3D models, skins and particle effects." I've therefore changed the ebuild to LICENSE="free-noncomm". Feel free to reopen if you disagree.