Short answer: If the spouse is a bona fide W-2 employee, listing them as an employee can help the group qualify (it adds an eligible employee). If they don’t actually work in the business, they’re a covered dependent (spouse).
It comes down to whether the spouse genuinely works in the business. A spouse who is a bona fide W-2 employee can be enrolled as an employee, which can help a small group meet the ‘two eligible employees’ threshold many carriers require. A spouse who doesn’t work there is simply a dependent on the owner’s coverage. The distinction affects participation counts and eligibility, so follow the carrier’s rules and don’t classify a non-working spouse as an employee.