We usually don't have the dogs outside, mainly because they like to pester anyone who is walking around the neighborhood. Frisk is just fine with it, we have both a riding and a push mower. I'm only allowed to use the riding lawnmower because I am banned from the push because of what I did with it last time.. Anyway, Frisk always wants to get in my lap and ride with me on the lawnmower, he loves it!
We have never had Ethan out while we were mowing, but he would most likely be terrified of the noise.