I think it depends on the plan. Some are, some aren't. But I'm pretty sure you'd need to specifically get yourself added to most plans, which will mean the spouse or the spouse's employer needs to pay more.
Your best bet is to look at the expat forum recommended by
@Mike D and
@Tipetoo.
Insurance plans are not all equal, read this and make sure your friend gets a plan that will cover his/her insulin without requiring changes every couple of months.
https://www.nytimes.com/2019/01/18/opinion/cost-insurance-diabetes-insulin.html
And there's a "grey" market just for test strips.
https://www.nytimes.com/2019/01/14/health/diabetes-test-strips-resale.html
