An employer maintains a DB & a DC plan and the two plans are aggregated for 410(b).

DB plan covers the Owner and owner's Spouse [spouse was included to pass 401(a)(26)]. Spouse took a nominal salary for plan yr 1 and accrued a benefit. For plan yr 2, the spouse took no wages and as a result did not accrue additional benefit during plan yr 2 (because her average comp was halved – benefit formula is flat % with fractional accrual).

For 401(a)(26), did the spouse benefit under the plan for plan yr 2?

You might get away with it, but I doubt it would survive an IRS actuary's audit.

I would add a provision to include a minimal additional benefit for the spouse.