Does Apple allows restricting In-App Purchase DLC Non-Consumable Content to one device?
You are afraid Apple will reject your app because you use non-consumable content on only one device? 

One of my project has in-app purchases only for 1 device. The app is already 6 years continuously reviewed and successfully deployed. Believe me, this is not an issue aslong you are not using a subscription. 

The only problem you are facing is someone can buy the DLC also on a other device and it will auto unlock as it has already been purchased with the same Apple ID. There are ways to prevent this by securing your app via a database.