I installed a new disk drive (moving my original from hda to hdc and installing the new drive as hda) and decided to try a "gnome workstation" install onto the freshly installed disk. My original disk had a linux partition (redhat 6.1 /) and a linux swap partition on it. The gnome workstation install ended up changing my original linux partition into a swap partition, thus wiping out my original linux environment.
Yes, the intended purpose of a Workstation installation (as is documented in the installation guide, as well as in the online help during the installation) is to take all of the free space and existing linux partitions and use those for the installation. So, the installer was working as designed.