I've always used Snow-Seal on my holsters (and everything else made of leather, for that matter.)
BUT! I do seem to recall a thread here some while back where Ray suggested what to use and it wasn't Snow-Seal.
I'd contact Ray and ask him what you should use. After all...they're his holsters and he should know what's best.
I was also going to recommend contacting Ray. I believe he recommended using a neutral shoe polish to me if I had any squeaking, but mine hasn't been too noisy.
The squeaking sound results from friction between the holster and belt. This usually stops after a week or two of use after the holster has been broken in.
The friction can be relieved with any waxy substance applied to the belt and holster attachment points. Neutral shoe polish works well. Snow Seal has a high beeswax content so it should work well. Some folks report good results with talcum powder.