Hiya.
Orc's are imaginary... humans are not.
Reiterating, what you do in your own home is your business - I'm talking about published works.
Folks have already brought up the Thermian Argument, haven't they?
The fact that orcs are imaginary really isn't relevant. All characters in fiction are imaginary! If that defense held water, then you could always do whatever you wanted with any fictional representations without reproach, but that is empirically not the case. Symbols matter to real humans. You'd have to go much further, and establish that there's a clear line of "imaginary enough", that magically makes it okay. Good luck with that.
In the end, you have one or more real-world humans who have
made a choice to depict a thing that looks and operates a whole lot like real-world racism. Why would anyone really want to do that? Make a world that mirrors some of the worst elements of our own, and not for the explicit purposes of having characters fight against that aspect?
Because it is simpler? That's a privilege argument - since we are in a position in which we can ignore it, we will do so, because that is more pleasant. That's either ignorant, or pretty explicitly choosing to disengage your empathy and respect for those who cannot ignore it, because they live it.
Ignorance isn't a sin, and can be rectified. But, once informed, willfully choosing to disengage the empathy is... not a good look. Do that publicly, and you deserve a heap of criticism for that.