If you install Parallels Tools version 9 within the RHEL 7 guest it will work. Parallels version 8 complains that the Parallels Tools version is out of date and the Ptiagent64 (Parallels Update Agent) errors out, but other then that everything appears to be fully functional. The mouse works, the display is not fuzzy, and shared folders work... that's all I really care about.
If you're wondering how to get and install Parallels Tools version 9, when using Parallels Desktop for Mac version 8, here is how:
1. Download a copy of Parallels Desktop for Mac version 9:
http://trial.parallels.com/index.php
2. Mount the downloaded dmg disk image file by double clicking on it.
3. Open a Terminal session, on the Mac host, and run: cp -p /Volumes/"Parallels Desktop 9"/"Parallels Desktop.app"/Contents/Resources/Tools/prl-tools-lin.iso ~/Documents/Parallels/"Parallels Tools Linux Version 9.iso";
4. In parallels, connect the cd-rom image that you just copied to ~/Documents/Parallels/Parallels Tools Linux Version 9.iso to the guest, i.e. Parallels > Devices > CD/DVD 1 > Connect image... > Documents/Parallels/Parallels Tools Linux Version 9.iso
5. In the guest, the cd-rom should automount, so just open a terminal session and run: sudo /run/media/*/Parallels\ Tools/install