Ehh, you can do it that way but if you only do Group 2 and Group 4 the dimmers can get out of sync. The best way is Groups 3 and 4, then on one dimmer set Parameter 12 to 11.
For this to make sense, we have to dive into what actually happens on the Z-Wave side of things-
Group 2 sends BASIC_SET commands- ON and OFF. BASIC_SET is the simplest, most basic Z-Wave command that exists. It will work on almost any device, including things like water valves and door locks.
Tap the top or bottom of the paddle and it will send a BASIC_SET on or off command to Group 2.
If you associate in ONLY Group 2, the associated device will come on and off when the paddle is tapped, but won’t dim at all.
Group 3 is SWITCH_MULTILEVEL_SET. SWITCH_MULTILEVEL basically means a dimmer switch- and rather than just ‘on’ and ‘off’ it’s a number from 0-99. So whenever the switch’s level changes, either by tapping the paddle or holding it, the new level is sent to the associated device.
Tapping the top or bottom of the paddle sends a SWITCH_MULTILEVEL_SET 0 or 99 value to Group 3. Holding the paddle to dim will send an updated dim value (between 0 and 99) to Group 3.
If you associate in ONLY group 3, the associated device will come on and off when the paddle is tapped, and after you dim the main dimmer the associated dimmer will react and change to the same level, but it won’t live dim as you hold the paddle down.
Group 4 is also SWITCH_MULTILEVEL, but it’s ONLY for live dimming. Holding down the paddle and releasing sends a SWITCH_MULTILEVEL_START_LEVEL_CHANGE and SWITCH_MULTILEVEL_STOP_LEVEL_CHANGE.
If you associate in ONLY group 4, the associated device won’t react when the paddle is tapped, but holding down the paddle will cause it to dim up and down. For that reason, Group 4 should be used together with either Group 2 or Group 3.
The main difference between 2 and 3 is 3 will keep the dimmer actually in sync. With Group 2+4, if the devices have different ramp rates, or if the start and stop dimming commands are delayed a bit, it’s easy for the two dimmers to end up at different dim levels.
However for 3 to work you have to (on ONE dimmer) set Parameter 12 to be 11. Do this FIRST (before you associate). Without it you get a loop where the dimmers keep trying to update each other as they ramp.