I haven't used the NB minimus shoes with a pack cause I don't like them, but I have used fairly minimalist shoes with a pack in the back country. Some of the early minimalist shoes (talking what was avail 5 years ago) weren't so good because the soles didn't have lugs or other features that gave reasonable tracking on common terrain I encounter. I nearly killed myself wearing a pair of vivo barefoot sneakers that have great traction on roads, but where useless on pulverized dirt trails.
These days there are numerous minimalist shoes (including some of the nb minimus I believe) which have soles which should work on trails with packs. My current goto shoe is the Inov-8 Trailroc 245 which isn't the most minimalist shoe (it has a 6mm heel, and 6mm of sole) but seems just about perfect for me. Works great with my >=30lb pack.
My personal experience is that when weight got up to 60lb, I wanted more support from my shoes, but that might be because I hadn't strengthen the foot muscles for that level of a load.
–Mark

