First of all, you would have to submit a W8-BEN-E, not a W8-BEN. Since we're talking about a company account.
(Or maybe you would have to submit a W8-BEN as well? But definitely the W8-BEN-E for the company.)
If you claim treaty benefits on that form, you are lying.
You don't have access to treaty benefits with such a setup.
You would have to check the line that you don't claim treaty benefits, and then you get 30% WHT.
Say you have a US LLC (transparent) that is owned by an
offshore company, for example a
Hong Kong Ltd.
The US LLC is transparent, so it's irrelevant for taxes.
So the situation will be the same as if the
Hong Kong company owned the shares.
But the
Hong Kong Ltd. does not have treaty benefits: You would probably want it to have tax-free status, which would mean it is not tax resident in Hong Kong.
But even if it was, LoB clauses in the trax treaty would state that the company does not have access to treaty benefits.
The only way this could work is if you made the Hong Kong company tax resident in your country of tax residence.
In that case, it would of course get access to tax treaty benefits like a local company. But then why bother with the two companies? You could simply set up a local company and then open an
IBKR account for that entity directly. No need to overcomplicate things.
Typically, the offshore company would be tax resident where you live (assuming you live in a developed, high-tax country). So then, strictly speaking, maybe it's fine to claim treaty benefits.
But the thing is - you would still have to register the offshore company in your home country and pay tax. You're even literally telling the
IRS: "The Hong Kong company pays tax where I live!"
If you don't do that, then you will be committing tax fraud in your residency country.
TL;DR: It's either not legal or there is no advantage over just using a local company.