As a fallback I imagine so yeah. I'm trying to think about what would be going on at the time, wondering if unexpected instructions inside a form would be confusing.

Disclaimer: I don't know how a screenreader would present this, example only

"Form entry. Input name. Input email. Ignore this field it's for spambots. Input url. Submit" -- In this case does the message more naturally apply to email or url? I'd imagine there'd be a pause after input email (to wait for the input)? I need to set up a screen reader :)

And then hide the warning using CSS too, so it gets picked up by screen readers just like the hidden input!