CATIA V5 surfaces are not true NURBS. They act like NURBS but the math behind them is different. Rhino’s surfaces will often break apart at patch boundaries when exported to CATIA and vice versa. Otherwise I have had no problems using surfaces from either software when imported into the other other.
The older CATIA V4 was Bezier based and had a tolerance of just 0.0039 inches. Fixing gaps was a way of life using V4.