Looks like there's a reason, chimney, roof etc., looks like a giant rodent was gnawing on the block and clay flue tile LOL ! The only thing that would concern me is if you laid the ladder flat, and used it as a pick or its in the section,(as if it were a beam) where it could possibly buckle if placed at a wide angle with only the ends bearing on the ground and the structure, not sure what the splice will allow, but for the job specific purpose like often times is the case, mother necessity becomes creativity, would work for me. I see ladders often enough on CL, hit or miss on good prices etc. and listings but its a fairly common item often times very reasonable, but nothing was available, and it was badly needed seems to be a logical solution.
Like the safety railing, and technically there should be osha approved plank, pre-engineered pick or what have you, I still thought 2" spruce was always fine, as long as its cut for the purpose, not cracked or weathered too much. we used to sell units of it at the lumber yard. 2 together would load a small car on a flatbed. Toe boards are also something to consider, at home, small residential job, not such a big deal, just keep people away down below when working, it helps keep something from dropping off the edge, gives ones foot a reference point of the edge, and its a requirement on big jobs. Just the railing alone is a big help though, most importantly, that is something I don't like to skip.