Sorry for distressing you. But I am afraid you will get only opinions and guesses here. The real scrapers are unlikely to show up here and talk business.
On that other sites the situation might be vastly different due to how they handle tags and how accurate those tags are. Filtering for the #noai might be their most reliable option.
On Itch the manually added tags would not change filtering in the case that someone were to filter for no-ai. Things will appear in the tag no-ai either by manually selecting no-ai or by filling out the ai disclosure with "no".
If a scraper bot looks for tags onpage on Itch, that means the bot creator knows about Itch tags and can just as well use inbuilt tag filter system to prefilter the input for the scraper. Would be a lot more accurate too, since the 11 tags are not really meant for meta information.
And from a player's perspective (mine), seeing no-ai (as a tag) is not informative. That's the default. It is not information. If any, I want to see detailed info about ai-usage and not about non-ai-usage. I do also not see that a renpy game was not made with unity and not made with rpg maker and that no puppies were hurt in the making of it. I like the ai disclosure information on Steam with the detailed info, and that is only shown, if there is ai things going on.
If a dev cares for these things and want's to make a statement about how no ai was used, I would prefer this to be positivly worded. Saying that it was hand crafted by the developer. Or commissioned with links to the artist, or whatever. no-ai can also mean pictures drawn in sweat shop by child labor, to exaggerate. A lot of people that want to avoid ai, do so for ethical reasons. Not having used ai does not equate that the things done there were created ethically. And I know a professional studio that was very unethical like not paying artists and such. At least that's what I heard about that studio.