Is it harmful for Dogs to eat cat food?

Yes and no.

My dog eats almost everything that fits in his mouth from pizza and leftover to my neighbor's dog ****. But gets a slight kick in the face when doing that last bit there. In good health so far.

Yes and no is correct so far as I know, but for a different reason. Dogs can eat cat food with no problem, except that cat food tends to cost more. Cats should not have dog food. Dog food runs to a higher ash content. Now, I'm not perfectly sure what "ash content" really means, but it does tend to have a bad effect on the cats' more sensitive urinary tract - especially the males.