ONLY if each of the dimmer racks has their own isolating switch as required in Health (Public Buildings ) Regulations 1992 section 44. Switchboards (3) Lighting dimmers shall be connected in the active conductors and an isolating switch shall be provided for each dimmer bank installed and where a resistive type dimmer is used the isolating switch shall be on the line side of the dimmer.
The three phase splitter must use two switched three phase outlets connected in parallel, you cannot use two three phase sockets without switches.
If you draw too much power you will trip the circuit breaker for the three phase outlet on the wall. Most switchboards are locked to ensure that the circuit breaker is not reset until the cause of the excess current is found and removed. The resetting of circuit breakers may only occur during normal working hours, so if you trip a circuit breaker during a show, you may not be able to use that lighting for the rest of the show(s).
You need to ensure that the maximum load or wattage on each phase does not exceed the 3 phase outlet circuit breaker rating. You need to make a list of which light(s) are on each dimmer channel for both dimmers and add up the total. 2400 Watts is 10 Amps.
When doing a Square One lighting design, you ideally want one light per dimmer channel for maximum flexibility of the design. If you are using 500W lights, then you will have 12 x 500W = 6000W or 6kW per dimmer rack. As there is 2 dimmer racks you will have 12kW maximum load which is 50 Amps total for all three phases or 16.6 Amps per phase. Three phase outlets for dimmers are usually 32 Amps or 40 Amps, so with one 500W light per dimmer channel, you only draw half of the power available.
For 24 x 650 Watt lamps the total is 15,600 Watts which is 65 Amps total for 3 phases, or 31.5 Amps total per phase which does not exceed the current rating of the circuit breaker.
If you want to use some 1kW lights, you will have to reduce the number of channels you use and balance the load across the three phases.