The Revolutionary Army isn't really doing overly good job if that big muscle brained man managed, while being wounded to boot, sneak aboard one of their ships and stay hidden all the way to the HQ. He can't exactly hide in a barrel, unless it's a barrel for giants.

As for why Blackbeard would be interested, it's of course for the fruit powers and physical possessions the revolutonaries would have amassed. Blackbeard can steal powers, after all, and stealing riches is pirates' main job.