In your opinion That's the five who were named. The sixth wasn't. In my opinion. You should read the discussion in the link provided above if you haven't already.

From the novel:

"The representatives of the Five Families of New York were the last to arrive and Tom Hagen was struck by how much more imposing, impressive, these five men were than the out-of-towners, the hicks."

Clearly, Don C. had already arrived, and was not one of the five.

And the physical description...

"The five New York Dons were in the old Sicilian tradition, they were 'men with belly' meaning, figuratively, power and courage; and literally, physical flesh, as if the two went together.... The five New York Dons were stout, corpulent men with massive leonine heads, features on a large scale, fleshy imperial noses, thick mouths, heavy folded cheeks. They were not too well tailored or barbered; they had the look of no-nonsense busy men without vanity.

Except for the cheeks, he's not describing Vito.