Late Child Support Payments
If the x-husband has paid all child support due and owing by December 31st he is current for that taxable year, and thus, able to take the deduction.
Although he is consistently late, if he eventually pays up, I wouldn’t file a contempt, since it is costly and time consuming.
If he is consistently late and that causes your wife hardship, it may be worth filing a contempt citation.
If he is unemployed and doesn’t have wages to garnish, you can garnish his bank accounts or lien his house, if he has these assets.