兵士の気節に於るが如く means not "like the moral backbone of soldiers" but "like in the moral backbone of soldiers" or "similarly to the case of the moral backbone of soldiers". (気骨 is a fairly rare word and I don't know if 'moral backbone' is the best translation, but let's leave it for now.)
- が如く is roughly the same as の如く, and they mean "like ～" or "similarly to ～". が was a possession marker in classical Japanese. It follows a noun.
- 於る【おける】 is a perfective attributive form of 於く【おく】 in classical Japanese, but you probably know this as a fixed grammar pattern. For now, please know that attributive form of a classical verb worked as a noun, and this pattern sometimes appears in modern Japanese, too. So here 兵士の気節に於る is a noun phrase meaning "the case/situation of the moral backbone of soldiers".
Likewise, 社会民主党などといふ場合に於けるが如く in the example you found means "as seen in the case where people say something like 社会民主党".