So there's nothing to prevent a moral objectivist from affirming that normally, stealing is wrong, but in special cases it may be justified. Indeed, 'particularists' go even further, and claim that there are no (useful, informative) moral principles at all. One can still be a moral objectivist, and hold that each particular ('token') action is either objectively permissible or impermissible, depending on the precise details of the situation in question. They're merely claiming that we can't usefully generalize from the moral status of token actions to general act types. This suggests that morality is complicated, but complexity is obviously compatible with objectivity. As I put it in an old post:
Any adequate theory must be sensitive to the morally relevant features of a situation. It would be morally obtuse to claim that lying (for example) is always wrong, no matter the specific context. But this isn't relativism, so long as we agree that there's an objective fact of the matter in any particular case. Some lies are permissible and others aren't; but there's no one particular (token) act of lying that is at once both right and wrong, "relative" to different observers.
One might object, "If you can't give a straight answer to the question whether lying is wrong -- an answer that's true for everyone, in all times and places, then isn't that practically the definition of relativism?" But no, that's just as stupid as demanding a straight and universal answer to the question whether cats are tabby. The fact is: some are, some aren't. In each particular case, there's a perfectly objective fact of the matter. It may vary from case to case, however, rendering the general question underspecified. (Which cat? Which instance of lying?) Point to a cat, and I'll tell you whether that one is tabby. Likewise, point to a particular instance of lying, and we may determine whether that action was wrong or not. Any more general questions may lack answers. This isn't "relativism", in any interesting sense. It's just the perfectly ordinary point that (to put it in slogan form) variation precludes generalization.
General lesson: to think clearly about such fundamental issues, focus on tokens, not types.