I do not understand how, as Solaris was open previous to Oracle's acquisition.
Red Hat does not maintain all of the code in RHEL - they repackage and patch everything taken from other developers. Very few packages are authored solely by them.
I don't know what relationship Oracle has with the current owner of the UNIX System V source (appears to be The Open Group), but Oracle is responsible for vastly more of the kernel and userspace in Solaris than RHEL.
Red Hat does not maintain all of the code in RHEL - they repackage and patch everything taken from other developers. Very few packages are authored solely by them.
I don't know what relationship Oracle has with the current owner of the UNIX System V source (appears to be The Open Group), but Oracle is responsible for vastly more of the kernel and userspace in Solaris than RHEL.