I would still consider that to be a contribution structure that doesn't comply with the uniform election rule component of the Section 125 nondiscrimination rules. The EE-only tier isn't providing a uniform election with respect to employer contributions for the non-HCPs, and therefore it's discriminatory in favor of HCPs in that tier. I'm assuming it's the same underlying medical plan option(s) at issue for both groups.
Your argument that the salaried employees with the 100% ER contribution effectively aren't part of the cafeteria plan at that EE-only tier because they have no contribution is a creative one (kudos), but my feeling is the IRS would consider it too clever by half.
That would be my position here.
No real way to answer this definitively since guidance is limited (and enforcement experience is essentially nil), but for what it's worth I would advise the client to change that structure.
The workaround I'd suggest is that there is never any issue with providing a greater taxable salary/wage to employees. If the salaried EEs were paid a greater amount intended to cover the increased cost of coverage, the salaried EEs could then make an election to apply that extra amount on a pre-tax basis to the employee-share of the premium. That would put both parties in largely the same position as if they had received the larger employer contribution.
I put out a couple of posts diving into this topic that might be interesting/helpful:
https://www.newfront.com/blog/designing-health-plans-with-different-strategies
https://www.newfront.com/blog/nondiscrimination-rules-for-different-health-plan-contribution-structures-2
Here's the relevant cites:
Prop. Treas. Reg. §1.125-7(c)(2):
(2) Benefit availability and benefit election. A cafeteria plan does not discriminate with respect to contributions and benefits if either qualified benefits and total benefits, or employer contributions allocable to statutory nontaxable benefits and employer contributions allocable to total benefits, do not discriminate in favor of highly compensated participants. A cafeteria plan must satisfy this paragraph (c) with respect to both benefit availability and benefit utilization. Thus, a plan must give each similarly situated participant a uniform opportunity to elect qualified benefits, and the actual election of qualified benefits through the plan must not be disproportionate by highly compensated participants (while other participants elect permitted taxable benefits)…A plan must also give each similarly situated participant a uniform election with respect to employer contributions, and the actual election with respect to employer contributions for qualified benefits through the plan must not be disproportionate by highly compensated participants (while other participants elect to receive employer contributions as permitted taxable benefits).
Prop. Treas. Reg. §1.125-7(e)(2):
(2) Similarly situated. In determining which participants are similarly situated, reasonable differences in plan benefits may be taken into account (for example, variations in plan benefits offered to employees working in different geographical locations or to employees with family coverage versus employee-only coverage).