Defined benefit accrual for sole proprietor

In a plan with 500 hours required for the annual accrual, do you think it is reasonable to credit an accrual when there is no net earned income  ?  Likewise, is it reasonable to not credit an accrual on the basis of "no income, therefore not 500 hours?  Would you look at gross income before deciding on an answer?  Any IRS input on this question? 

I don't work on sole proprietor plans, but it seems to me that the number of hours worked can be more than 500 even if there is no net income.  It's a defined benefit plan, so unless the accrual is tied to the specific compensation for the plan year (i.e., a cash balance plan or a plan where the monthly benefit accrued for a plan year is x% of that year's compensation), one would count the year as having been earned if the plan's minimum hours of service requirement has been met.

A sole proprietorship where the sole proprietor has neither earnings nor hours sounds like it is probably defunct.

As it is for a sole proprietor, why is there a minimum number of hours of service in the plan provisions that the sole proprietor cannot satisfy? 

Does this plan have other participants?

My understanding is that the IRS will need some evidence of substantial employment activity in this type of situation.  Can the participant demonstrate that they were actively working to make income, as opposed to fooling around with a hobby?  Work logs, email evidence, office rental, business cards and phone, contracts with clients that may not have been paid yet, proposals to prospective clients?