If you do not change any of the CentOS RPMS with your added content then it would be fine to use the official CentOS branding and installer. Your content as well as ours (the entire compilation) would need to be GPL compatible with sources available, etc.
We don't change any CentOS RPMS, and all added RPMS are distributed under GPL license.
I assume you are changing at least /etc/redhat-release and other things if you are shipping a "distribution" though, so the above is likely not true. If you replace CentOS content with your own, then we would request that you change the branding for the installer.
We don't neither replace the /etc/redhat-release from the RPM: after the first boot there is a simple bash script which changes the redhat-release link.
In the end, I think we can use CentOS name and logos without re-branding.
Thanks for the support.