They might not drop out specifically because of Haskell, but I don't see how it wouldn't be a contributing factor. The Haskell course here was pretty much just a struggle for almost everyone that took it.
I've met a lot of people (at work and post-grad) who have graduated from colleges without an idea of what a functional language is or the concepts behind them. I don't blame them, but its a pity to find so many workarounds in legacy code which could have benefited from functions as parameters and less state in general.