Well doesn't just doing the math makes sense? If I'm starting with one capsule that contains 1 billion live organisms (1 x 10^9) and bacteria double between 9 and 20 minutes at room temperature - we'll say 20 minutes - then in one hour there are 8 billions organisms, 2 hours 64 bil, 3 hours 512 bil, and at just 4 hours there are 4.1 trillion organisms spread throughout your substraight. Multiply THAT exponentially times the remainder of 5 days or 116 hours and then divide by how many total ounces of cabbage you started with (I use two 1-quart jars) and well, please get your calculators out to double check since it's been awhile since math class but that's one ounce of kraut with a hell of a live organism count.
And yes, adding the capsule does change the flavor and the probiotic count and flora type from what is referred to as "wild fermentation." Cabbage has some lactobacillus in it naturally, so you don't need to use a capsule to get a fermented probiotic. However, if you want to grow specific strains of bacteria - I know that some people are sensitive to different ones or just want a wide spectrum, then you can use a capsule to control that. I like to KNOW what's in my kraut, personally, and there is much less risk of contamination.
I've done my own experiment at home. I did one jar with half a capsule and one without. After 5 days, the one with the capsule definitely smelled and tasted more vibrant and pungent, and had a brighter color. The one without any starter added smelled ok, but did not taste as good and was not as crunchy for some reason - though maybe it just needed a few more days to ferment.
Anyway, here's a fun link on on "wild" fermented kraut without starter and their bacteria count and scientific analysis. (*Note their charts are in milliliters, roughly 1/30 of an ounce.)