The overall latency says nothing about the sync precision required. The displays need to be synced and the graphics cards need to have their vsync synchronized between them (usually via dedicated hardware). If the displays are out of sync, you immediately get visible tearing at the seams.

If your parallel renderer divides the image along a grid that does not correspond to display boundaries, you need to gather and composite the partial framebuffers after rendering them. This means that you're now sending frames across the network amd you need to take care that you aren't compositing frames from different timesteps, for example, because the the part of the rendered framebuffer that goes to compositor/display node A arrived in time, but the part going to compositor/display node B somehow didn't.