I use a mountain bike ('95 Marin team) hardtail to bike commuter, and also long distance (road) touring and find it works for me (plus, I'm to cheap to buy a real touring bike).
However, I find the longer wheelbase MTBs to be better because they will be more stable on the road versus the short wheelbase ones that are more for "east coast singletrack" so-to-speak. Best thing would be able to try them out loaded and see what works best but that is usually not an option. I use Old Man Mountain racks front and rear on my Marin. I use a QR rack for the front which has an old Marzocchi Bomber Z1 fork on it and the back, I use a OMM red rocks which mounts to my V-brake arches on the seatstays.