Can I create an In-App purchase item for tvOS game only?

Yes, it'll still show in iTunes as an in app purchase, but unless you include it in the list of IAP IDs you request in StoreKit in your iOS version it won't show in that app. (or even if you do request it, you don't have to display it in the app itself).

It's worth giving your Apple TV IAPs recognisably different IDs to the iOS ones for your own sake when editing them and maintaining your code.

Also, if you're doing Universal Purchase (so players who buy your iOS version get the Apple TV version) it's worth considering whether you want a different IAP for each device. (feasibly you can allow the tv IAP purchase to unlock things on the iOS version and visa-versa when you restore purchases).

I am not sure if an un-balanced iap would be allowed. Anyway, I will have a try.

Thank you very much.