Can you use a gravel bike on the road?

Yes, easily. A gravel bike is happy on pavement, just slightly slower than a dedicated road bike because of the wider, grippier tyres. Many riders fit a second set of narrower road wheels or tyres so one bike covers both fast road days and off-road adventures

Is a gravel bike good for commuting?

Very. The wider tyres soak up rough city surfaces, the mounts take racks and mudguards, and the relaxed position is comfortable day to day. It's a genuinely practical commuter that's still fun at the weekend.