Orion, not really sure about the differences in the ballasts concerning the affect on the circuitry - I just kinda threw that out there. You're actually better off building your system with the worse case scenario in mind anyhow. If all is right, the system should be able to switch a heavy inductive load up to the capacity of those contactors.
I agree with TomGeorge about powering the JD-VCC separately, but just make sure the grounds are connected together. In fact double check all grounds.
If it were me, I'd still try the movs on the 24v lines, since even though the relays would take the shock, there could be stray noise associated with those lines.
Another, "just putting it out there thing," is to be sure any digital signal lines (such as i2c, spi, etc) - you mentioned "sensors" - that could tell the arduino to create the change that's being seen are completely clear of the power-switching lines of any sort - a/c or d/c - and especially away from the lines going from contactor to ballast.
But, with all that being said, seeing TomGeorge's "karma" at 984, and mine being at just 1, I may not have been so good at helping people solve their problems here (I think that's what "karma" is about here), so maybe best to just wait until he gets some sleep and comes back with more ideas for you. 