There is no difference between "low" brass and "high" brass in so far as the support of the shotshell is concerned. Modern shotshells get little, if any, real support from the their "brass"...which is actually a thin layer of steerl that is brass plated. I cannot say if there is a difference in two loads without checking the figures, but if both of yours are WW LR slugs, my guess is that they are the same or nearly so. I would also guess that Winchester used the white hull and low, nickle plated brass to positively ID the LR slugs from previous lots, both during production and in the field. Why, I have no idea. I imagine the nickle actually provides a bit more protection from rust (yes, shotshell "brass" will rust!) than the brass coating used in other rounds.

I do not know of any agency having issues with the WW LR stuff, but that does not mean it has not happened.