I do not understand completely what exactly you are trying to do.
A sad story is that the ST platform does not support dimmers, esp rotary dimmers. There is even no good UI representation for this type of devices.
As far as I know, the best thing you can do is to connect the dimmers to the Zigbee network and bind them directly to the light groups.
Binding to Zigbee groups is not supported officially either, but there are community drivers (NEW RELEASE) Beta Edge Driver Zigbee Light Multifunction Mc - #33 by Mariano_Colmenarejo.