You still don't need PoW here, though. All the servers are presumably trusted. You perhaps have a trust issue with your employees, but that is what access controls (limit the number of people who can create items) and audit logs (after an item is created, you know exactly who did it and when) are for.
And yes sometimes an employee that you've trusted with item creation access will turn out to be a bad actor, but you have the audit log to prove that, and you fire them. That's... just life. Hopefully the fact that there are audit trails dissuades most of the borderline-sketchy employees that it's not worth the risk.
> adding a few seconds of PoW makes the resulting chain so hard to forge for crime-of-opportunity style attacks (preventing internal employees from making untraceable gold
I just don't get why this needs a blockchain. Internal access controls! Don't just let random employees make arbitrary, untraceable changes to game state! Of course you're going to have problems if you allow this, blockchain or no.
Obviously you are much more knowledgeable about the issues around transferring state across server boundaries. But I still have not seen anything (in general) that suggests that inherently centralized systems (like an MMO run by a single corporation) meaningfully benefit from PoW systems. PoW is just there to ensure that people can't forge things. But when your ledger is centralized, if you implement the proper access controls and audit trails -- which you should be doing no matter what -- then PoW/blockchain is just not necessary or useful.