Ni el tato

Ni el tato
 

I think it means nobody, but I'm not completely sure. I read this in a Spanish newspaper. Is this a term used outside of Spain?

You're right about the meaning, Poli.
It would mean something like "not even John", "John" being someone unimportant: not even someone unimportant would be there (or would do something).

It's not used in Mexico, but I guess it would be understood in context.
I think the first reaction would be "¿Y quién es el Tato?", which is what seems to be intended too. :)

"Ni el Tato" makes sense because Tato is a nickname. It'd work that way everywhere provided there is some Tato dude to leave, but as a set expression I've never heard it here in Argentina, though you can say here "no va a quedar ni el Cacho" or "ni Cachito" or "ni el loro" with the same purpose, being "Cacho" a nickname not used in the highest levels, as the article "el" shows.

agree with both. "tato" is a nickname. Common in Spain
another similar "Ni Dios"
ejemplo:
Hoy juega la selección de fútbol. EN la calle no estará ni el Tato /no estará ni Dios

SAludos :D