Ok, I'm getting a handle on this now.
(1) USERRA says a returning employee has a right to make up accrued benefits "derived from, employee contributions
or elective deferrals" subject to the 402(g)(3) exclusion. (Translation: The returning employee has a right to make up either:
employee contributions {to a money purchase plan}
or
elective deferrals {to a CODA}.)
(2) Now, the question regarding "picked up" employee contributions is: are "picked up" employee contributions only "employee contributions" in form, but "employer contributions" in substance?
I think the answer depends on the context within which the question is posed.
(a) From a tax perspective "picked up" employee contributions are employer contributions.
(B) From any other perspective "picked up" employee contributions are employee contributions that happen to be "picked up" by the employer.
If you were to ask our retirement board, our employees or our employer,
"who makes the picked up 5% salary reduction contributions to our money purchase plan", everyone would give you the same answer; "why the employee, of course!"
The 5% employee contribution, matched by our employer, is 5% of the employee's actual pay. If the employee makes no pay that pay period, no contribution is made.
(3) Under this type of plan, I don't think USERRA requires an employer to make up contributions with no salary reduction. I think USERRA requires the employer to allow the returning employee to make up forgone employee contributions based on the pay she would have earned, (or her average pay for the 12 months prior to her military service, etc. etc.). And the employer, in this case, would have to match those make up contributions.
(4) I think the employer could pick up these make up contributions despite the their "elective" nature if it followed certain procedures.
The election(s) the employee would be required to make would be:
one-time, or made once a year
irrevocable
for a sum certain (up to the total of USERRA-covered forgone contributions)
for a period certain (how about a minimum of 1 year up to the lesser of 3 times the period of USERRA-covered military service or 5 years?)
The employer should probably obtain an IRS Private Letter Ruling permitting the arrangement (similar to PRIVATE RULING 200118056).