Fedora is mostly based on Gnome and GTK, but yet there are people who prefer KDE. On a pristine install, during package customization, I removed the "Gnome Desktop" group, and added "KDE Desktop". On first start, I noticed that the GTK applications look very bad (like early 90's squared Gnome), and not similar to either Clearlooks (default Gnome theme) or Plastik (default KDE theme). Installing gtk-qt-engine makes GTK apps appear fine (with Plastik theme). One may argue this is not important, but considering all Fedora system management applications are GTK/Gnome based, they look pretty bad on KDE-only systems, this this improvement makes a difference on end-user experience. This has been reported for 8. I don't know how KDE 4 will work on Fedora 9, so I don't know if it will still be valid in the next release.
Sorry, I don't think having different settings depending on the package selections on the DVD is a good idea, nor that the folks working on the DVD will be happy about that. We may consider using gtk-qt-engine on the installable KDE-Live spin where such customizations are easily possible. One problem is that gtk-qt-engine currently still uses Qt 3, so you won't get the shiny new Oxygen look anyway (but Plastik or whatever style you selected for Qt/KDE 3 apps). But I'm afraid that for the generic installer DVD, such KDE-specific customizations are simply not an option. By the way, if you want the default Fedora GTK+ theme, make sure you leave the Nodoka theme enabled in your package selections.
An easy solution, without modifying the installer, would be adding gtk-qt-engine as a Requires to kdebase. But then again, I don't know how that would behave with KDE4.
gtk-qt-engine is kde(3) only.