You wouldn't build a datacenter directly on top of the supervolcano. It's in a national park, after all. Any sort of relatively minor incidents from the geothermal plant wouldn't affect datacenters located outside the park (and they could be a few hundred miles away, if need be). The degree of devastation from an eruption would be so great that the normal risks associated with "hey, build sort of near a volcano" don't really apply in the traditional sense.