Is it a HIPPA violation for a health insurance carrier to reveal to an employer if an employee has single or family coverage?

1. It's HIPAA, not HIPPA.

2. No, its not a violation. Assuming that your medical insurance is at least partially paid by your employer, and/or that you pay for a portion of your coverage through payroll deductions, then your employer has a need to know this information. Why do you ask?