Not really. Smoker entire mindset is the one who is more likely to change the system from the inside. Smoker will most likely never quit the marine, but like Koby, he will probably do what it takes to change this system from inside. Nothing shows us right now that Smoker even have the idea to quit. And we would need some setups for that to happen.
There are a lot of good marines. Coby and Smoker always stood out among them. At the same time, Coby stands out only as a friend of Luffy. His storyline is secondary. It is logical that these two do not have the same role in the plot. It is logical that they may just be on different sides of the Marine, since they are so singled out.
Coby always dreamed of becoming a marine. While Smoker has been thinking about the honor of a pirate since childhood. It was the thought of this (that there were no such noble pirates as Roger) that contributed to his joining the Marine. That says a lot. The whole Smoker's storyline is based on how he gradually changes his views about pirates and about the Marine. Moreover, the current situation simply leads him to a moral collapse, when he will no longer be able to do anything else but leave the Marine.
I hope that Smoker's role is more than being another kind marine on Luffy's side.
In our theories, we should be guided by the analysis of the plot and characters, and not by what they directly said (or thought) that they wanted to join Luffy. A huge number of nuances indicate that Smoker can really join. The last nakama is a very responsible mission. It really must be very difficult mentally and very emotionally. No other candidate is capable of giving this.