I remember awhile back, people started noticing that archived pages of Reddit* had a 'logged in' status and showed the account name Archive was using to scrape the data. Not sure if this is how it works with other sources.
*I think it was Reddit.
*I think it was Reddit.
Personally, I also suspect that archive.is is simply paying for subscriptions as a last resort, but I specifically wanted to know from OP. If they do, they do remove the "logged in" status. It always appears as "logged out" in the archived version. I wonder how far they go, whether they scrub watermarks and other identifiers.
e.g. https://archive.ph/8ZDI7 a page removed from original website, archive.org has paywall, but archive.is is somehow able to "archive" it paywallless