Beth, the OP feels that they ARE "legally" married per the laws of the state in which she resides. I believe they may very well have been. My earlier response was based on my contempt for people who think that it's just a piece of paper. But, realistically, if they are considered married by the state of PA, and they reside in PA, then there is no fraud involved. The insurance company is wrong.
No, the insurance company isn't wrong. They are not obligated to recognize common law marriages or those couples who "feel" they're married. The carrier and employer get to define who constitutes an eligible dependent. For the great majority of insurance plans, that is the legally wed spouse of the participant and his/her dependent children. (Some employers/plans choose to recognize domestic partners; a very few municipalities require that eligible dependents include same-sex domestic partners.)
The insurance carrier in this case can pursue the employee and OP for fraud if they wish to because the OP's "spouse" signed her up for insurance benefits when she didn't meet the definition of an eligible dependent in the plan. The employer could also terminate the OP's husband if they wished to for falsification of company records.
All that appears is going to happen is that the OP has been dropped from coverage which they ought to thank their lucky stars for.