Considering a job with a health insurance provider. Should I be concerned that my employer may have access...?

... to my family's health history and knowledge of medical expenses? Normally, individuals' information is not shared by the insurance carrier with the employer, but when the carrier IS the employer... well you get the idea. I'd figure it would be a trivial exercise to figure out which employees are costing such a company the most and to... deal with said situation accordingly. Not that anybody in my family is planning on getting sick of course, but I wouldn't want a future hospital stay to be the cause of my dismissal.

Challenge: I'm sure there are laws in place to protect employees of health insurance providers, but what actually happens in practice?

they may or may not hire you. i have never been in this situation, but had a similar one. I switched my company's personnel over to a professional employment organization (PEO) where we were all leased. I was not told why we were rejected, but later came to find out (when she went to the hospital) that one of my employees had a terminal illness and this was the most likely cause of not being taken on. After she quit the company, I again applied to that PEO and was taken as a client.
So..even though the employer does not have access to specific health data (HIPPA), they are still told by the carrier that a certain company or individual may be too great a risk for insurance purposes.