Do any newer production aircraft use venturis as a backup vacuum source?
Not as far as I know. Even Vacuum pump systems are quickly becoming a thing of the past. Electric AI's are available and I have seen plenty in use. However with glass cockpits making their way into general aviation AHARS units are becoming more and more common place over traditional vacuum systems. There are even some small drop in units intended to replace traditional vacuum systems like DG's and Attitude Indicators. Venturi vacuums, while simple have down sides like potential icing risks and needing sufficient airflow to function.