I've never used that tool (and don't plan to) so I don't know. If they just embed the content in an iframe or something then there's no issue (but then there's no need or point in scraping). If they're just scraping to train then I think you also imply there's no issue. If they're just copying your content (even if the prompt is "Hey Perplexity, summarise this article <ARTICLE_TEXT>") then that's vanilla infringement, whether they lie about their UA or not.