from my research (on tPF), the rain/stain repellent sprays like ScotchGuard, Wilson's, and Apple Garde are fine on most leathers. do a test on the bottom of the bag first, if you want to make sure. it seems like the cleaners and moisturizers/lotions have adverse affects on certain leather types (making them darker or dull).
i have two RM MAMs and i'm confident that the sprays will not harm the bag. i'm hoping that this pretreatment/repellent will mean i won't have to use those cleaners or moisturizers!!