are stove top griddle only for gas top stoves?
This question isn't straight forward as there are so many types of electric stove/cooker tops. It would depend on whether you have radiant rings, sealed plates, halogen, ceramic or induction hobs.
Induction rings will heat any ferrous material (iron pan) but works better with a flat bottom.
Other than in the case of induction if the griddle fitted well and had a flat bottom for good thermal contact it would work fine but the shape of your cooker top might make this difficult to find.
Many types of hob would get scratched by an ill fitting griddle where as gas fittings tend to be quite heavy duty.
I have a cast iron 'griddle' for stove top use. I use it on my electric range and it works fairly well, but if there is any foodstuff on the stove it gets baked on and is hard to clean, so I have to scrupulously clean the stovetop first.