Of course it's true that someone could say that Marx was an “essentially a fascinating figure.. from whom we can learn a great deal” and not be a fan - politically or ideologically - of the dead German. But if that someone is Jeremy Corbyn saying these things, then that's something else entirely.
What is it, anyway, that Corbyn thinks we can learn from Marx? If he were specific, what would Corbyn say? Most people now think that as a futurologist or prophet, Marx proved to be a joke. (Socialists don't think that.) Most people believe that Marx's economics are stuck in the 19th century. (Socialists don't think that.) Politically, most people think that Marxism is very dangerous and indeed deadly. (Socialists don't think that.) Though as a prophet of a future utopia and a stern moral critic of capitalism and capitalists, even Marx's critics can see the religious appeal. (So can socialists.)
The Islington North MP also said: “Marx obviously analysed what was happening in a quite brilliant way and the philosophy around Marx is fascinating.”
And as a Marxist socialist, I suppose that it's almost inevitable than Corbyn will think of capitalism in 19th century terms. After all, that's when Marx was writing. Thus when Corbyn also said that “[t]he [Conservative] Government's policies... are a return to the workhouse” he was being a gross rhetorician – as Marx himself was.