Gravely warranty covers averything but the engine on their machines. Yes, the selling dealer should be set up with the engine manufacturers to do warranty work on the engines their mower lines use. You would be surprised how many dealers are NOT authorized to work on engines.
So, if you have an engine problem, Gravely can not do much about it. It is the dealers responsibility to work with the engine manufacturer to get the engine problem solved.
I do agree with you about Kawasaki engines. I like Kohlers myself.