The whole skeletons learn naturally thing is a bug with the latest version. The fact that ironbone skeletons can't learn those skills is because skeletons aren't SUPPOSED to be able to learn non-combat skillz through any means besides inscription. At least, not above a 1% learnrate. The normal skeleton caste doesn't do that because of a bug/mistake. But the upgraded skeleton castes work properly.
I would say it'd be worth it anyway to upgrade if the skeletons actually seemed to gain some advantages from being armored up. I've watched as a kobold thief with a large copper dagger calmly beheaded a dreadnought and then ran off into the night.
I know that only the bones are metal now and not the connections, but since they have such ridiculously low combat skills (dodge, armor user, and shield) then they just get chopped apart by even the weakest of opponents. Heck, I saw a dark strangler pull all the arms off of a bloodsteel skeleton not too long ago.
I know that they're a level 1 monster and not particularly capable, so I don't normally bother to infuse them. Slapping on some cheap copper mail seems to work just as well or better. Particularly the mail hood that keeps them from being beheaded.