I do sanitize by soaking the containers in a bleach solution and warm water for about 20 minutes. You can also buy commercial sanitizers, but bleach is cheap and effective. I also sanitize the equipment that I use (bowls, pitchers, spoons, etc). Snowdrift has an at home test kit, but I ran across a site the other day that offered pretty affordable testing (I want to say it was $25 USD a sample). I'll see if I can find it again.
I *think* that Germaben II can be used in scrubs, but don't quote me on that. I think that the oil phase has to be greater than 25% of the total formulation for one to use Germaben IIe. I'm sure you could research that. Phenonip and Optiphen might be an additional alternative.
Aubry gets away with using just ROE and other antioxidants because it's like that the organization is making an anhydrogenous scrub .. aka, not water in it. Theoretically one could get by with this; the problem is though, think about where you use a scrub... in the shower ... where there's water that will likely be introduced into the formulation. When you introduce water into the forumlation you have to worry about mold, mildew, and yeast .. those are just the things that you'll find growing in there. You can't even see the bacteria. I understand that many people want to use a natural preservative; I do as well. However, until someone comes out with something that's both natural an effective (so that I can protect the health and well being of my customers) then I'll have to stick with the synthetics.