I've seen people do this with short comics or short novels--like not their entire library of web things, especially long running ones that are still being updated--but if they have a bunch of readers already, it may perk some of their interest to buy a short story or a short comic from gumroad to own that is a completely finished thing, and not something they have to wait week to week to read. But if you don't have a bunch of readers on social media, I'd probably hold off on it. Like I might do that with a short comic one day, but for right now I think it wouldn't get anything in sales for me as a digital book.
Another route is the "pay what you want" option on gumroad, most will just download it for free, but you could get some dollars that way from people that tip. As for if the other novel hosting sites have paid books--I don't really know how those work, haha, but I imagine it's a lot of the same.