Not recommended on any Boeing FADEC airplane as far as I know......
Under the Boeing 737 Classic Supplementary Procedures Adverse Weather heading: "Moderate to Heavy Rain, Hail or Sleet", it mentions "Consider starting the APU (if available)" . Presumably this is a wise precaution against the possibility of a double flame-out in severe weather. On a personal note, when departing or descending towards an area of severe thunderstorm activity, this writer would elect to leave the APU running for take off and climb, and start the APU on descent before entering such areas of weather activity. It was considered good airmanship in case of a dual flameout in heavy rain. After all, there have been several recorded cases of dual flame-outs in severe weather. .