I've just booted the latest Mandriva in Virtualbox to confirm this, as I haven't looked for a while, and the GIMP is indeed in the KDE only live CD. It's not much of a stretch to assume that double clicking in "Install on Hard Disk" will also install the GIMP. In fact their much vaunted Control Center is a GTK+ app, which I never really see advertised anywhere.
As far as I can remember Mandrake/Mandriva have always installed both toolkits by default. They have never installed KOffice by default (thank god).
At installation you can select BOTH Gnome and KDE, and it works very well. I have been using Mandriva as my main Gnome desktop for quite a few years, and the integration issues are so rare that I don't remember any of them.
I think that the little KDE4.0 glitch and the temporary Gnome default install had a bit to do with that.