Again, I don't know what your game design is, but needing to replicate anything at the milisecond level between players and have it matter is a terrible idea, and if your game design requires it, I would rethink the design. Regardless of whether you do it with particles or with an internal engine graphical feature, it's the replicating that data between players that will be the issue, not the graphical rendering or particles.
Bouncing actual real time rendered lightsources off of water at the graphical level is a thing reserved for the Cry Engine (which I honestly don't even know if it does). :-) If it's actually a necessity to your game design, then you could just use math, have there by two lights at all times, player controls light A, collide at x calculated distance, *do something*, angle of incidence, procedural change light B to point off in new direction, etc.
But personally, if I was your producer, I'd probably just cut that feature and make you do something else. of course, if I was your producer I would have cut making an MMO focused on water in the first place. :-P