How do I wire LED light based zone for DALI dimming?
Nearly all drivers on the market will only occupy one "short address" even if they can drive multiple LEDs, lamps or tubes, so they will drive them to the same level. Any driver which is different, occupying multiple "short addresses" would probably make that clear in their information since it is unusual although valid.

How you split up your downlights over different drivers depends on what level of control you want. If you will never need to control the downlights independently, then you can wire them all to the biggest driver you can find, or in groups limited by the driver capability but either way, in broadcast mode, all together. If you want individual downlight control, you need an address per downlight, which means a driver per downlight, and some way of setting up the addresses.