No, these are not the same guys. These guys really are Cubans. Louis, Jorge and Umberto appeared in the episode The Cheever Letters
. Kramer met them at the Cuban Embassy (which doesn't really exist)in NY when he went looking for Cuban cigars so that he could trade the cigars to the golf pro at Westchester Country Club in exchange for golfing privileges. Kramer had lost all his other Cuban cigars in the fire at the Ross's cabin.
The Dominicans that you are referring to were in The English Patient
and did end up rolling crepes too tight in the Mandelbaum's restaraunt. These are the guys Kramer had Jerry bring back from Florida.