All Apple software works on almost all Apples.
But... if you are referring to the Installer disks, then yes, emac is for emac and imac is for imac. Apple likes it that way.
If you mean iLife, iWork
or other Apple sfotware, or for that matter, any software, all you need to do is make sure you have the correct specifications required by the software.
ie; Some video applications will run on most Macs, but if you don't have Firewire, then your camera won't sync.
Some applications require a certain processor, like a G3-800 MHZ or better and xx amount of ram.
These would be the only reasons that the apps may not work if your system is below the specs required.
So, short answer... if it is an installer that came with an eMac, then no it will not work on an iMac. But if it is an iWork/iLife disk, then yes, it probably will.
I hope this helps. If it does, please click Accept. If not, reply back to me.