Nipped by baby tiger during cub petting. should we be worried about rabies? barely broke skin, no bleeding but wound about 2 mm exists.

Doubt it: Zoo cubs are generally kept away from any possible rabies exposure and if young, the mother would have passed on some antibodies from her shots. Given the value of these animals they get better care than many humans. You should check with the Dallas health department for guidance. They maintain regional data on rabies activity in the area and also control much of the available vaccine.