I don't know what offset is, but the backspacing looks right. remember more backspacing=tires closer to the inside of the wheel wells.
I think you've got a good point that it won't matter much- with your lift you could run 33x12.50 tires and not have issues, so your comparatively skinny 285's shifting a little be here or there isn't likely going to lead to any rubbing.
My experience with the hub centric/shank wheels is all the load is still on the lugs. The hub gets is close, but there's always a little shift when I run that first lug down inside the rim. However when removing the lugs, the rim does kind of stay in place doesn't it.. On back of my Taco, I have to smack those with a BFH to get them to pop free after all the lug nuts are off, but on the 80 everything just falls off.
But regardless, you can run either style rim as long as you've got lugs to go with them. IOW I don't think there's a stronger side load lug out there for conical rims.
82 fj40, 99 uzj100, 06 gx470
97 DR650, 05 525EXC, 01 XT225, 09 TTR125, 07 TTR90, 07 CRF50