If your spouse signed a contract that said something like he would have to repay all or part of the signing bonus if he did not work for the company for a certain length of time, some people will argue that that alone is enough for him to know he did not have an unrestricted right to the money (it was restricted by the requirement to work a certain length of time). Your argument is also possibly reasonable. I have not researched Tax Court cases to see how such cases generally are handled, when the taxpayer makes the claim and the IRS disagrees, and I'm not a tax attorney.
