See the following. In general, if the switch dims by reducing current, you use it with dumb bulbs. They might be Dimmable LEDs, but the bulbs themselves are not networked.
If the switch dims by sending an instruction via zwave or zigbee to the hub, the bulbs can be either smart or dumb, it just depends. But if the bulbs are dumb they have to be directly controlled by a smart switch that reduces current (it just doesn’t have to be the same switch that sent the original request).
If the switch dims by sending instructions directly to a smart bulb to dim itself (but doesn’t change current flow from the switch), then both switch and bulb are probably zigbee.
Most smart bulbs for home use, including Philips Hue, GE link, Cree connectable, WeMo smart bulbs, and Osram Lightify are zigbee.
There are a few other brands that are other protocols, do check when buying.