If you have a QDRO (qualified domestic relations order), and if DFAS will honor it and split your retirement pay and issue a separate 1099-R to your ex-spouse, that is definitely the way to go. It is cleaner, simpler, and hassle-free.
There is no alimony "credit". Alimony is tax-deductible to the payer and taxable to the recipient only if the divorce was final before January 1, 2019. For any divorce that was final after January 1, 2019, there is no tax deduction for alimony. If you receive your entire military retirement benefit and then send part to your spouse because of an alimony order, you must pay the income tax on the entire benefit. There's no way to make your ex-spouse pay tax on their share of the benefit. (You could try and argue to the family court that the alimony award should be reduced, since you have to pay all the tax. But there is no way to make your spouse pay the income tax.)
For a divorce that was final before December 31, 2018, where you can deduct alimony and your spouse must report it as taxable, there is no financial difference between doing that and submitting the QDRO to DFAS. I would still submit the QDRO as that makes the whole situation much easier for you. You don't have to keep sending checks to your ex because DFAS does it, and you don't have to argue with your ex about taxes since DFAS will issue a 1099-R.
