Navarre/Nafarroa is considered as Basque land by many, but not by all. Certainly there are some towns and cities in the region which are pretty Basque strongholds - Leitza, Lekunberri and Goizueta in particular spring to mind. They even fly the Ikurriña on the town hall of Goizueta. Even in the mostly Spanish parts of the area there are those that identify themselves as Basques. In its simplest form, the lands claimed as Basque are: Bizkaia, Gipuzkoa and Alava (País Vasco), Nafarroa (Navarre), Lapurdi, Nafarroa Beherea and Zuberoa (Pays-Basque). Only the former three are the official Basque country.
Sicard and Cazaux are both French Basques, hence why they're in the Basque team.
For the record, here's what I think is an exhaustive list of riders from outside País Vasco who have raced for the orangemen:
Íñigo Cuesta (Villarcayo, Burgos) 1994-5
Thierry Elissalde (Bayonne, Lapurdi) 1994-5
Roberto Lezaun (Pamplona, Navarre) 1995
David García Markína (Pamplona, Navarre) 1996-7
Igor Flores (Urdiain, Navarre) 1996-2002
Unai Etxebarría (Caracas, Venezuela) 1997-2007
Ángel Castresana (Medina de Pomar, Burgos) 1998-2001
Peio Arreitunandia (Villa de Cruces, Galicia) 1999-2000
Iker Flores (Urdiain, Navarre) 1999-2006 (brother of Igor)
Rubén Díaz de Cerio (Logroño, La Rioja) 2000-3
Samuel Sánchez (Oviedo, Asturias) 2000-11
Patxi Ugarte (Pamplona, Navarre) 2001
Egoi Martínez (Etxarri-Aranatz, Navarre) 2002-5, 2008-11
Gorka Verdugo (Etxarri-Aranatz, Navarre) 2004-11
Alan Pérez (Zurucuain, Navarre) 2006-11
Jon Bru (Vera de Bidasoa, Navarre) 2007-8
Jorge Azanza (Alsasua, Navarre) 2007-11
Juan José Oroz (Berrioplano, Navarre) 2007-11
Javier Aramendia (Funes, Navarre) 2008-11
Mikel Nieve (Leitza, Navarre) 2009-11
Pablo Urtasun (Urdiain, Navarre) 2009-11
Daniel Sesma (Pamplona, Navarre) 2010-11
Romain Sicard (Bayonne, Lapurdi) 2010-11
Pierre Cazaux (Saint-Palais, Baja Navarre) 2011
How many of them would I say aren't Basques? Beyond Sánchez, probably none?