Do I need a hinged knee brace if I've never had a knee injury?

Generally no. If you have healthy, stable knees and are skiing recreationally or even aggressively, a quality soft or hybrid knee pad provides sufficient impact protection without the cost, weight, and restriction of a hinged brace. Hinged braces are designed for joint stabilization, which uninjured knees don't need. The exception is competitive racing at high speeds where the forces involved exceed what healthy ligaments can withstand in worst-case scenarios.