The name of the middle eastern salad containing Tomato and Cucumber

If you are really set on doing this, just use the same amount by weight or volume, preferably peeling the tomatoes first. (Cut an x in the bottom, dip in boiling water for 10 seconds, pull off the peel). You'll have plenty of liquid coming out of the tomato, don't worry about that. But honestly, I don't recommend doing this. Fresh tomatoes that are any good are so good uncooked that it is a waste, and fresh tomatoes that aren't good won't get better by cooking them. Even Mario Batali says you should use canned tomatoes for cooked sauces.

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.