I don't think Shichibukai take orders from anyone. They are still pirates, only government sanctioned ones to hunt down other pirates (that would make them privateers). Rather than orders it should be more like specific contracts. If they actually took orders, it would indicate they are a solid part of the World government hierarchy, and I deem that would make their role in relation to the artual navy problematic. So, a certain degree of ambiguity is to be expected from them, Kuma included.

Admirals of course are a different matter, and no doubt they already needed to prove their obedience to the ideology and (ruthless) loyalty before they even were made admirals. I doubt you become an admiral simply by eating a powerful fruit and waltzing in. While there could be individual differences there, it would be surprising if they all weren't 100% supportive of the World government's absolute rule.