Yes, yes it is.
Even if it was disgusting, even if you didn't agree with it, it should be allowed. If only so that you can prove just how stupid it is.
Yeah no, they shouldn't be publishing hypothetical racial slurs in their game just to appease some hypothetical backer.
And again, censorship is still wrong. Even if it is abbhorrent, people should be allowed to say it, so that people who are smart can refute it.
I'm not saying racials slurs are a GOOD thing, I'm saying if someone spent upwards of 500 dollars, and there was no refund coming, then yes, in this hypothetical situation, he can put what he wants in his gravestone.
As I recall the Kickstarter, Obsidian always reserved right-of-approval over backer submitted content. You didn't pay to have a specific text included. The opportunity to negotiate the content of a memorial was part of the reward for specific tiers. It was never a backer right to force the inclusion of offensive text. Whether the specific text in question should have been allowed is a separate issue, but I think all the pontificating about backer rights is out of place.
So by this logic, didn't Obsidian already approve of this piece of content?