I did that because of the first error message "xxx conflicts with xxxx" I wanted to remove the old driver first, because rpm -Uh --force file_name did end with that message too. So i cannot install the new package before removing the old one. I'm also thinking like you, but as i said i want to have Xorg and all the other rpms working after the update.
If package "fglrx" supersedes "fglrx-glc22" then really the packager should have included an "Obsoletes: fglrx-glc22" tag in package "fglrx". This would have allowed an upgrade to "fglrx" to remove the old "fglrx-glc22" package.
One way you can check that "fglrx" can safely replace "fglrx-glc22" would be to check what the two packages provide.
First, look at what your installed "fglrx-glc22" package provides:
$ rpm -q --provides fglrx-glc22
Then see what your new package provides:
$ rpm -qp --provides fglrx_6_8_0-8.10.19-1.i386.rpm
If the latter is a superset of the former then you *should* be OK to get rid of the old one and add the new one in as a replacement.