With the EMH you have the argument of multiple persons put into him and meticulously crafted, just like Data.

With Vic Fontaine... that's just the basic operations of the system.

IMO Vic is likely like the EMH and based on a real person.

Bashir mentioned that Vic was created by a programmer called "Felix" - we don't specifically know how he created him, but in a mirror universe episode, "Vic" is there, except he's not a hologram, he's a real guy (who gets killed), and he doesn't respond to being called Vic.

My headcanon is that that was Mirror Felix, and Vic is modelled after his creater a la EMH.