The topic of whether a self-employed individual is or is not an employee if the individual has no (or negative) income for a plan has come up when discussing plan administration. This has been an issue in particular for purposes of coverage and compliance testing. There is no conclusive guidance, with closest direction is to be consistent in treating the individual for all plan purposes and this would tie into the individual being otherwise treated as an employee. I expect this is also the case for determining service.
With respect to elapsed time rules, the a period of severance of less than 12 months will be included in elapsed time service. One could build an argument that having documentation that the SE individual was compensated for one hour of service would be enough to continue the accrual of elapsed time service. This would not be invalidated if the net earnings from self-employment at year end was zero. I note that being available for service differs from actually performing an hour of service (unless there is some form of on-call compensation). While SE compensation is deemed earned as of the end of the plan year, there is no deemed service rule other than the service spanning rules (including certain leaves of absence, military service...)
Good question, with pathways to differing conclusions.