From what I have seen, people do it both ways.
On my 45g, I have one pump for my skimmer and my return pump runs (3) filter cylinders, a chiller and a UV sterilizer. On my 220g (in progress), one pump for skimmer, one pump for (3) filter cylinders and my return will feed a chiller and UV but, my UV will only be used when needed.
You separate the flow with (3) valves, one in between the in/out of chiller, UV, etc to direct/restrict flow and the other two to shut off for maintenance. If you really want to know the gph of each you could use flow meters that either Neptune or GHL offer, if you happen to be running a controller.