Good question. I'd hope/expect that you could, but that doesn't mean much.

no you can't use pro in the harness.

That is disappointing. I find myself mostly using Codex these days. ChatGPT still for one off questions/prompts, but usually complex problems require context, like files and tools I already have on my system, and Codex is way better for that.

I think pro is really subsidised and they don't want to encourage it in the harness.

That's an odd choice. I wonder why.