Hmmm, I don't think they are one and the same... but because Astarion is my favourite character, I can't resist the lure of a good theorycrafting/character analysis thread.
So several days ago I mentioned while giving feedback that I think Larian is trying to pull a fast one and I made the prediction that Astarian is really..... wait for it..... waaaait for it..... Cazador.
1. Astarian is constantly seeking to control the parasite, to learn how to use the new power that the parasite is giving the group. Power and control are what True Vampires live and feed off of, other than blood. To dominate one's mind, actions, and existence is what they get off on. Vampire Spawn simply do not have that mindset as they are nothing but puppets as Astarian points out many times.
He wants to control the parasite because power and control, to him, mean survival. Let's assume that he is who he appears to be, a vampire spawn who was a slave, and now finds himself free. It makes complete sense to me that he would clutch at any bit of power that he can, to survive and stay away from his abuser. He has also likely taken on parts of Cazador's controlling personality as a mask to wear, because - let's face it - if he's only known someone else's power and control for 200 years, then to him, that is how the world works.
Also, have you heard his response to a certain dialogue choice you can make when you talk to him after your tadpole dream, when he first tells you about having been a slave, and you tease "I didn't know you had a master in the bedroom" or something to that effect? Holy crap. Normally he enjoys cheeky responses from your character, but his response to this in particular was so angry, so hurt, so well-acted that I had to re-load my previous save and NOT choose that option again! He may be secretive/evasive about some things, but his responses about having been a slave and having been abused are very telling, especially in this scene. I certainly think his story is exactly what it appears to be.
2. Wait a minute. If Astarian was a True Vampire then he wouldn't be soo weak in the game you say??? And you would be correct to say and think this. However, there is one line in all of the dialogue with Astarian that just keeps sounding off in my head when I think about this possible MAJOR rope-a-dope by Larian. It was brief and well hidden but there is a moment when Astarian says "Somebody has changed the rules". Yes I know he said it while explaining why all the downsides of a Vampire seemed to not apply to him but I feel that how he said it was a HUGE hidden clue as to what we may see in the future.
I took that line to mean The Absolute or whoever is responsible for the tadpoles, has changed the rules. He hasn't changed the rules himself.
I don't know what the rules for vampires are in DnD, I'm coming from more or a literary/mythology background here, but he does explain clearly that he's surprised he can enter homes uninvited, walk in the sun, but still can't cross running water. Those are all age-old vampire lore things.
Also, IF he was a true vampire, biting your character would mean he has turned you into a vampire spawn - which has not happened. He doesn't have that power.
3. Now this part is just me theorizing as I have only ever encountered the Monster Hunter once and Astarian was a corpse in my camp from when Halsin jumped me for wiping out the Druid Grove on my evil playthrough. Why would a monster hunter have interest in small time prey like a spawn.... a puppet... no, I think he knew more about his Mark and he was after the big man... Cazador and he had put the pieces together himself. It kind of reminded me of a Van Helsing vs Dracula type of feel
The Gur monster hunter was tasked with bringing Astarion back alive because of the demonic inscription on his back. It appears to be part of a puzzle to be solved later on in the story.