I do not see how if it's a huge skimmer with 20 dart NW pumps or a small skimmer powered by a single sicce 2500 pump that it matters. Dirty water is.... dirty water! Feed a skimmer water that has more crap in it & I would think no matter how the skimmer is designed (1 pump, 2 pumps, 10 pumps) it would pull more stuff out.
Maybe I should shoot Jeff over at ER a email/PM to see what he has to say ....
They recommend using a feed pump with Euroreef recirculating skimmers. I discussed the issue with several ER people (Chip & Jeff) when I first purchased my skimmer and when I ordered a replacement part last Fall. ER is a small, family business. You are right, dirty water is dirty water, whether you get it from direct feed or can capture it in a controlled area of your sump and feed it back to your skimmer. It is the same dirty, raw water (so long as you can capture it in a controlled area of your sump). I suspect if you have excessive air issues in your drainage pipes, direct feed would decrease skimmer performance. Or perhaps it has something to do with using multiple recirculating pumps and being better able to control flow (without excessive air) to the skimmer from a feed pump.
Once my system is up and running, I will post pictures of a glass of water collected from my drainage pipe before it is discharged into the sump and will post a picture of a glass of the same discharged water that is captured from the controlled area of my sump where the dirtiest water is collected.
Irrespective of what EuroReef, Spazz or Geo or others think, if one approach gives you better results on your skimmer than the other, then go with the method that gives you the best results.