You can, as part of an employment agreement which defines the total compensation package, provide that a person's base pay is permanently reduced by X amount which will be contributed as an employer contribution on the employee's behalf. Like plans that require employees to contribute as a condition of employment - the amounts do not count as deferrals.
However, providing annual discretion - which if you do with matching contributions that indirectly provides discretion - then I think you have a CODA instead. Unless with a match the maximum is assumed and "charged" whether he gets it or not.
Much easier to defend at the start of employment (or plan) - the total compensation package is X and it is comprised of base pay A, retirement plan contributions B and H&W benefits C plus whatever incentive pay is earned. If there's a waiting period then define up front these components before and after, because doing it only when the person becomes eligible looks more CODA again.
Of course, if someone takes a lower comp because of these "employer provided" contributions that are subject to a vesting schedule - that's another complication.
In summary: defining the total compensation package by component in employment agreement at employment commencement - good - reducing a participant's pay arbitrarily to pay for his matching contributions - bad.