It really has nothing to do with the GPL in any case. All distros are made up of much software that is not GPL (XFree86 is not GPL, Sendmail is not GPL, Perl is not GPL, etc, etc). SuSE has some sort of special license with Yast if I remember right and Red Hat has some sort of deal with their branding and trademarks (icons etc). I think with Red Hat it's only a problem if you want to resell their software. You can do it but you have to yank the Red Hat logos and remove the Red Hat name. Now if you give it away I don't believe you have to change anything, I believe you can make copies and give away as many as you want.
Here is the trademark guidelines for Red Hat:
http://www.redhat.com/about/corporate/t ... index.html
Now I haven't read the above in quite some time (and I don't have the energy to read it right now) so my assumptions about it may be way off. Better read it yourself and make up your own mind. If you hear back from Red Hat I would be interested to hear what they had to say.