It (homeworld source) wasn't GPL'd (or released under any FOSS compatible license, i.e., it's not open source). It was released under an RDN license - free to modify/use for non-commercial use. Relic retains the rights for the code released, and as well claims rights to use/distribute/sell anything produced with that code.
Since Relic changes their site organization periodically, the old links on RDN I have from DoW don't work. You can get the source, which includes the license terms, from google.
