No, when you install RHEL you get a choice, you do not have to have the gui at all or you can choose the ones on the disk or you can install another from RPM.
Just an FYI, you do not have to have the gui installed to use the gui installs for an app. All you need is a small subset of the libraries, not the whole WM. The client (Person doing the install) can use a lot of different software on their end, I am only going to point out two possible solutions. They can use cygwin and ssh with an exported X display then start the app install, or they could use putty and exceed in the same manner. Ether way it does not need to be a gui on the server. Heck with cygwin and ssh you can create a simple icon on the users desktop to connect, export the display, and start the application all in background so the user never needs to learn or use the WM on linux.