It looks like a pretty good platform in pretty good condition.
I don't know of any FEMA bus fleets in OR. The GSA has quite a fleet of buses used by the Job Corps centers in OR. Those buses get quite a workout every weekend shuttling kids from the centers to and from the I-5 corridor. The rest of the time those buses those buses don't get used very much.
Since they generally only put on 200-300 miles a week the mileage sounds about right for a bus of that age.
I would say that if everything the seller says is true then that would be a pretty good purchase.