Unlikely there would be an emergency. Secretaries of Treasury normally work more regular hours, so it won’t be a problem. He primary a budget maven not a banker, and he’ll probably have fewer problems than as the president’s “chief of staff” who might get woken up whenever there is a presidential crisis.
He is the first Shomer Shabbos cabinet secretary (under the Republicans Dov Zackheim was an under-secretary, albeit with a yarmulke in public). In Israel, Orthodox Jews have held cabinet positions, but they got them as patronage rather than based on merit.
“MO” means “Modern ORTHODOX” – he davens at a frum shul, keeps Shabbos and kashruth – that’s pretty much the basic definition of frum.