If it is possible to for the body to synthesize whatever material, it can create a frame for the bones, then wrap that frame in bio-active layers. Basically, a skeleton for the skeleton. Given the intricacies of other body organs (think the sizes and complexity of the eyes, says), such is not too hard of the task.

In fact, this probably answers all other concerns raised here. Corrosion and electric-conductive? A bio-compatible wrap (similar to enameled steel) solves that. Grinding between different bones? The ends of the bone can be built out of different material than the fragile length.

Furthermore, none of these concerns matter for, says, horns, especially the tips. Evolutionary speaking, it makes complete sense for animal to evolve steel-tipped horns: these steel parts hurt no one but their enemies.

(also note, carbon fiber avoids a lot of these bio compatibility issues).

In other words, animal kingdom did not have metal parts because synthesis is impossible, rather than because of disadvantages of metals per se.