The owner-spouse & partnership partner-spouse with no other employees is a specific requirement to be non-ERISA one-participant plan for 5500/EZ exception.
ASPPA ERISA Outline Book has it a bit more detailed than DOL section 2510.3-3. Any shareholder of any corporation (S corp & C corp treated the same) that are not owner and spouse would not qualify as a one-participant plan for exception to 5500-SF filing.
Any business arrangement that includes non-spouse owners would seem to be subject to 5500 filing requirements regardless of asset value.
