I have made testing using these SmartThings Edge Drivers that support Group Cluster.
Links to drivers:
Zigbee Button + Groups - Alpha Test - Devices & Integrations / Community Created Device Types - SmartThings Community
Using these drivers and Zigbee Group cluster, it is possible to adjust the dimming of the lamps with buttons and at the same time it is possible to get information about the presses to SmartThings.
I don’t know if MITTLED supports Group Cluster.