There is a whole range of tires suitable for buses.
Some are Drive tires, some Steer tires. Some are designed for all positions. Many are optimized for regular road surfaces, some do better than street tires on rough roads, or in snow.
Most street tires will be just fine on graded gravel roads (dirt roads), except maybe if it has been raining hard when there might be a lot of mud.
Talk to your local bus barn, or a commercial tire dealer. Tell them where you intend to drive and consider their recommendations.
You can save money with recaps on the drive wheels, but not on the steer wheels. Given Skoolie highway speeds, recaps should be fine.