As someone new to product marketing, and thinking of seriously recruiting at my own company's product marketing team (I'm currently in customer success, have an MBA in marketing), do you think taking Product Marketing online courses are beneficial?

I made a similar transition many moons ago when I working at Medallia. What helped me, and I reckon what will help you, is having an intimate understanding of the customers, their needs and how our technology uniquely solved their problems. The training you are getting in Customer Success will go much further in helping you build mental models that you will routinely use as a PMM, than external trainings. 

That being said, I did like doing the Pragmatic Marketing set of GTM courses when I was a freshly minted PMM. As to the one you are referring to, it seems new in the market, and I would still opt for Pragmatic Marketing until there is consensus that another program is clearly better. You could still be a great PMM without doing either, in my humble opinion.