From what I read of Gemma, I don't think they have any connections, but from what I read of Astoria, Blaise seems to have heard of her, but as he is not the type to reach out, he might not be able to make the first move to be friends.
Whereas Blaise knows Draco from school, obviously. Apparently, Draco went down the route Blaise is currently wishing he went down (Healer or Healing Potioneer). Considering Blaise regrets not staying in touch with his friends, maybe Draco and him can reconnect?