Smith, who has accumulated over 50 caps for the Stormers, is the latest player to join the expanded squad, after his provincial team-mate Ruben van Heerden joined the group last week in preparation for the double-header in Gqeberha.
He will report for duty with the rest of the squad in Johannesburg on Sunday, where they will resume their preparations from Monday after spending the weekend with their families.
Stormers teammate Salmaan Moerat was forced out of the group after suffering another long-term injury, while emerging Boks Ruan Nortje and Cobus Wiese are away with the Bulls in Ireland. However, coach Rassie Erasmus confirmed that stalwarts Eben Etzebeth and Lood de Jager are good to go, as is Junior Springbok captain Riley Norton.
The squad will depart for the Eastern Cape on Wednesday afternoon, with the Springbok and SA 'A' teams having their respective captains' runs on Friday for Saturday's clashes at the Nelson Mandela Bay Stadium.
Springbok coach Rassie Erasmus and SA 'A' team head coach Mzwandile Stick will announce their matchday squads on Tuesday.