Should an arson fire be covered under vandalism or malicious mischief if a home is currently unoccupied?

It typically depends on the proximate cause. If the fire started because a person lit it intentionally I would say it would fall within vandalism and malicious mischief. If it started on it own it would be covered under the fire peril. Unfortunately most policies exclude VMM coverage if the home has been vacant or unoccupied for a certain period of time.