Hey there! As far as running a crime syndicate goes, there are two options: your friend's character can either build a repertoire with Neal and begin working with him to spread out the distribution of contraband throughout the Cave; or the character can work on trying to break into the supply depots to acquire the items for themselves and begin running the contraband. The second one would require a lot more coordination, since getting other characters involved would probably need an IC campaign.

tl;dr: Yes, this would be allowed, just be warned that it would take time to either gain Neal's trust, or to find a way into the supply depots. Those are heavily guarded and secured, after all.

(Also, this was the perfect place to ask that question!)