I don't know that I've ever seen anything specific about Hubspot and GTD. I will tell you that most CRMs are hopeless as an effective primary GTD system for a number of reasons. First, they are rarely built to support freeform lists (you have a huge number of things in your life that have nothing to do with customers/clients). Second, they often get seriously overcomplicated with dependencies and collaborative features.
I would recommend a blended system using Hubspot for tracking CRM-type activities and get an external system (a list manager like Outlook, Wunderlist, Todoist, OminFocus, etc.) that tracks all of your projects and actions.