Do I need to add a tension crack to my RS2 SSR model?

Tension is handled differently in finite element methods (RS2) than in limit equilibrium methods (Slide).  If you use plasticity for the material, a tensile strength is defined for Mohr-Coulomb and implicitly defined for Generalized Hoek-Brown materials.  The material can actually fail in tension if the tensile stress exceeds the tensile strength.  So the zone of tension is automatically determined through the analysis, unlike Slide in which you have to manually define a tension crack zone.