As you already found out, there is no Classic app of the game on CD.
From the ReadMe:
Installing from CD
* Install SDL by copying SDL-1.2.X.pkg.tar.gz to your hard drive. Now
double click on it to decompress it. Now double click on the
resulting SDL.pkg file and the SDL installer should start.
* Copy the file called Dominions to your computer and run it by double
clicking on it. It can be run from the CD too, but it will run
Execute the file called win_inst.exe
As the ReadMe is from 2002, the game was probably meant for Jaguar or Panther.
Best try the game with Panther in Qemu PPC or with Windows (XP) in a virtual machine.
If you think of using XP you may send me a PM.