Thanks for your reply. I think the arrangement I described may be a group health plan, but it seems to me that there is a decent argument that it is not.
Here is why. Under the analysis adopted by some courts, the fact that the Donovan prongs are clearly met does not mean there is an employer plan for purposes of ERISA. See, e.g., Lanpher v. Unum (D. Minn. 2015) . In my case, the employer has no discretion or administrative responsibilities whatsoever. So, there may well not be an ERISA plan at all.
If the arrangement I described is not an ERISA plan, then maybe the arrangement is not a group health plan. As you know, a "group health plan" is defined under the ACA in part as being "an employee welfare benefit plan to the extent that the plan provided medical care . . ." It seems credible to take the position that there cannot be a group health plan if there is no employee welfare benefit plan, i.e., no ERISA plan.
Make sense?