Dimming multiple LED panels without PWM to LEDs; modified DMX control or something else?
Is this possible, 


Yes


  is the DMX to Meanwell architecture the way to go?


Use multiple Mean Well HLG-240-48A or HLG-240-48B  (cheapest cost per  watt)
The type A has a pot to vary the current between 50% and 100%.
Type B uses 0-10v, or a resistance to set the current. 

Use strings of 16 LEDs (white, blue, green) or 21 red in series (≈45v Vf).  Connect as many of the strings in parallel as each HLG can support.  Try to match forward voltages of the strings when connecting in parallel.

The parallel wiring will cause some current imbalance between strings.  If the forward voltages are not matched well enough you will need to add current balance circuits.  The easy way is to use an LM3466 with each string.  Keep the temperature down with good thermal management.