some examples of the lumpenproletariat given are people in organized crime, sex workers, and the unemployed.
Yes, though I don’t think that was a moral judgment of them so much as a description. Marxists are generally amoral—not to be confused with immoral. (I recently posted a video on amorality in c/philosophy.)
I’m not qualified to say whether Marx & Engels were right about them not being very useful in the revolutionary struggle. Perhaps the historical record of successful communist revolutions can show us. I also don’t know whether their analysis of lumpenproletariat in their place during their time would necessarily map perfectly to our place in our time. For instance, sex workers in the modern day… it kind of depends on which country we’re talking about.