My client as a defined benefit plan and a 401(k) profit sharing plan that covers ALL the Partners and Staff employees. The remaining employees (Associates) have a 401(k) plan with deferrals only. Can the compensation of the associates be used to determine the combined deductible limit of 25% + 6% of compensation? A former collegue has told me that the compensation used to determine this limit should include compensation from all employer sponsored qualified plans.

I believe that the limit is based on the compensations of only those eligible for the respective plans.

I agree. In this case with no ER contributions going to the associates' plan, they are not counted at all in the employer's deductible limit.

Can the compensation of the associates be used to determine the combined deductible limit of 25% + 6% of compensation?
I have not taken the time to look at the regulations, so FWIW, I agree with Blinky and mming. Does 404(a)(7) apply to the deferral only plan? Look at 404(a)(7)(C )(i) below. I would think their compensation is not included under the 404(a)(7) calculations for purposes of determining the percentage limit.

But with 2 DC plans in play, I am not 100% in this response.

IRC 404(a)(7)(A) IN GENERAL. --If amounts are deductible ... in connection with 1 or more defined contribution plans and 1 or more defined benefit plans ... the total amount deductible in a taxable year under such plans shall not exceed the greater of --

404(a)(7)(A)(i) 25 percent of the compensation otherwise paid or accrued during the taxable year to the beneficiaries under such plans, or

404(a)(7)(A)(ii) the amount of contributions made to or under the defined benefit plans to the extent such contributions do not exceed the amount of employer contributions necessary to satisfy the minimum funding standard provided by section 412 with respect to any such defined benefit plans for the plan year which ends with or within such taxable year (or for any prior plan year).
...
IRC 404(a)(7)(C ) PARAGRAPH NOT TO APPLY IN CERTAIN CASES. --

404(a)(7)(C )(i) BENEFICIARY TEST. --This paragraph shall not have the effect of reducing the amount otherwise deductible under paragraphs (1), (2), and (3), if no employee is a beneficiary under more than 1 trust or under a trust...

404(a)(7)(C )(ii) ELECTIVE DEFERRALS. --If, in connection with 1 or more defined contribution plans and 1 or more defined benefit plans, no amounts (other than elective deferrals (as defined in section 402(g)(3))) are contributed to any of the defined contribution plans for the taxable year, then subparagraph (A) shall not apply with respect to any of such defined contribution plans and defined benefit plans.

404(a)(7)(C )(iii) LIMITATION. --In the case of employer contributions to 1 or more defined contribution plans, this paragraph shall only apply to the extent that such contributions exceed 6 percent of the compensation otherwise paid or accrued during the taxable year to the beneficiaries under such plans. For purposes of this clause, amounts carried over from preceding taxable years under subparagraph (B) shall be treated as employer contributions to 1 or more defined contributions to the extent attributable to employer contributions to such plans in such preceding taxable years.

404(a)(7)(C )(iv) GUARANTEED PLANS. --In applying this paragraph, any single-employer plan covered under section 4021 of the Employee Retirement Income Security Act of 1974 shall not be taken into account.