I would suggest "outer suburban" rather than "rural", at least in current usage.I tried to tell her that Bogan was a derogatory term for the Australian rural white lower class - again she did not listen, as it did not fit within her existing mental frame.
A lot could be said about race and racism in Australia, but this is probably not the thread for it, as I don't know of any gaming or gaming-related texts that deal with or express it.
While I agree with you that cultural norms can vary, and sometimes unexpected, I also think that sometimes their meaning is relativelyi evident. To go back to the JRRT example, there is no cultural norm that explains why JRRT was not evoking racist tropes in those passages.
And if we go back to the OP, do orcs - in the sense of non-urban, warrior cultured, village-dwellers who prey upon (typically white) "good"/"civilised" farms and townships express a colonialist idea? My view is that it is fairly clear that they do. And of course it woudl be quite possible, in principle, to have fantasy stories about pastoralist and village folk fighting off exploitative conquerors who displace them from their lands (an inverse of "Beyond the Black River", my least favourite Conan story although I think that puts me in a minority). But that is not a standard D&D trope.
Whether the FRPG treatment of orcs should be looked at through the lens of Orientalism, or colonisation in Africa, or the Western (in this thread, [MENTION=21169]Doug McCrae[/MENTION] has suggested both) is a further question, about the way these tropes have been developed and expressed in different literary traditions.
And what follows from this fact about FRPG orcs, eg about game play and the design of game elements, is something I don't have a firm view about - that's not an easy question to answer (in my view). But my uncertainty in relation to this last question doesn't make me doubt my view that there is a fact here.