The license on it is GPL version 2, but in order to download it from
  their site, you need to "accept" the license via a CGI script, which
  makes it somewhat tricky to download in an automated fashion.

This is goofy, since the GPL is explicitly written as a "bare license"
(nothing else gives you permission to copy) rather than a "contract
license".

I don't see any problem putting the tarball up someplace else, other
than using up bandwidth.  They might not like it, but of course the
GPL quite clearly permits such redistribution.  Such a mirroring might
be perceived by them as rude, though.

-- 
        Greg Troxel <gdt@ir.bbn.com>