As we all know, we find out pretty soon in the story that Buggy and Shanks were both on the same ship. In the flashbacks you can even see Rayleigh breaking up a fight between those two and Scopper Caban fighting.
Later on in the story we find out that those two were in fact on the Pirate King’s ship.
So why would there be no devil fruit users on the ship of Gol D. Roger(at least at the moment of the flashback)? In chapter 19, the chapter with Buggy’s memories of his time on Roger’s ship we see him remembering when they found the devil fruit. Based on this, Shanks and the crew’s reaction seems like they haven’t seen one before, or the effects of a devil fruit.
“What?! Was it a fake?”
“Well the story of the devil’s fruit was a rumored story from the start”
I guess it’s pretty obvious that if anyone on the ship had a devil fruit power, they would say something like “Well, I guess we have to find out what power you got” or “Well, it had to be a fake one”. But instead they doubt the existence or at least the effect of devil fruits, which in my opinion suggests that they haven’t seen one before.
Obviously you can argue that it is really early in the story and Oda treated devil fruits like a real abnormalty and changed Roger’s crew since 1997 when chapter 19 was released, which will most likely be the case. Nevertheless based on current released chapters we can assume that there were no devil fruit users on Roger’s crew, at least at the time Buggy got his devil fruit powers.
*Theory by TGForrest