Ah! didn't look in the General forum, I just came straight into this one. Anyway I'd already found that topic you linked to. But I think it's incorrect: it says enginepath_win32="C:\Program Files\OpenArena\baseoa" but that didn't work, so I used enginepath_win32="C:\Program Files\OpenArena\"
Did you add the following to the shaderlist?
Yes ("common" was already in the shaderlist, btw)...although come to think of it I did that before fixing the enginepath_win32 parameter...so that might be part of the problem?
Seeing as Radiant is GPL perhaps a preconfigured version specifically for OpenArena could be made available to download?