In Gerard v. Orange Coast Memorial Medical Center (2/10/15) 234 Cal.App.4th 285 (discussed here), the Court of Appeal held that this provision contradicts Labor Code section 512 and is invalid. The California Supreme Court granted review of Gerard, and it is pending on the Court's docket.
In the mean time, Governor Brown on October 5 signed SB 327, which amends Labor Code 516 to provide:
Notwithstanding subdivision (a), or any other law, including Section 512, the health care employee meal period waiver provisions in Section 11(D) of Industrial Welfare Commission Wage Orders 4 and 5 were valid and enforceable on and after October 1, 2000, and continue to be valid and enforceable. This subdivision is declarative of, and clarifies, existing law.This is urgency legislation that takes effect immediately.
The text of the bill is available here.