We've been using out hiking backpack since our daughter was 4 months old, it is designed and safe to be used once baby has full head control. It is adjustable so the head support moves up and down and the seat keeps the baby's hips in the same position that the Ergo does. There are straps that provide support so the baby easily remains upright and is not expected to support herself in a seated position. I live in the Rocky mountains where people do a great deal of hiking, and everyone I know has used their hiking backpacks usually by the time baby is about 6 months old, if you get a good quality one the are designed to be used with little babies. I suppose it depends on the climate, but there is no way I could hike with my LO in the Ergo, we would both overheat within 10 minutes with our bodies pressed against each other in the summer heat and the exertion from going up a mountain.
I agree that one person will need the carry the vast majority of your camping gear while the other one mostly just carriers the baby and your daily stuff like water and snacks. When I take my LO for a full day hike I can easily fit our gear for the day in the compartment of our hiking pack but not too much more. I usually carry my rain jacket, a sweater and change of socks for me, change of clothes/rain gear/jacket/hat for baby, some diapers and wipes, sunscreen and bug repellant, lunch/snacks/water for me and baby, water and snacks for the dog. I wouldn't be able to fit overnight essentials like a sleeping bag or cooking gear.