Is it necessary to skim the scum off of fermenting pickles?
I make pickles similarly, but not quite the same way: I usually make half-sours, as even the 5.6% salinity of that recipe would be way too salty for my family's tastes. I boil the brine before using it, letting it cool before adding it to the cucumbers. I use a clear glass jar rather than something opaque like stoneware, which might change the mechanics a bit. The biggest difference, though, is that I add a slice of bread, which really gives the fermentation a head start. Usually, the pickles are ready in two days, three at most. Perhaps it's this shortened time period, but I've never encountered any scum that needs to be skimmed off. Sometimes, if it was a particularly hot day or something, there will be mold, either on the bread or on the liquid; if this happens, the pickles are thrown away — it's just not worth the risk. 

That said, scum does not equal mold. If it's anything other than white, and/or if it's fuzzy, it's mold, and I personally would not eat whatever it occurred on, unless of course it was rotten moldy milk blue cheese. If it's really just scum, then it's probably a cosmetic issue: if you don't skim it off, the brine might turn cloudy and unappetizing.