It is necessary to have a generator in a 5th wheel, I know some have them some don't. We are looking to go to a 5th from our class a and we really don't use ours a lot now.
With the onboard Onan generators, you can buy a wireless remote start that is programable. Even in a park with electric hookups, you can program the remote start to activate if the power goes out so your pets will be safe.