Under what circumstances might my employer legally disclose my personal information to third parties?

The short answer is -- yes. In Utah, both parties are required to disclose financial information, and each can subpoena records from the other, should the party so desire. But, you say third parties, but you don't say who those third parties are. Yes, disclosure to your spouse's attorney can be required; and, if there is a financial expert appointed in your case, then to that expert. There are really no third parties in a divorce, just you and your spouse. So, I really don't understand who the third party might be.