If you pay your ex for survivor benefits, which are not deducted from the pension payment, is that amount deductible?

If you are paying your ex-spouse to maintain survivor's benefits (SBP) on their military pension, the payments would not be deductible. That is a personal expense, not covered by any current tax deduction.

(There would be one exception - if you were required to make that payment to your ex-spouse as alimony).