Coverage testing with union employees

I have a 401(k) plan where the employer has many union employees covered by a collective bargaining agreement. The union employees are currently excluded from the 401(k) plan. The owner is covered by the CBA under a separate union agreement, along with only a few other employees. For a little background, about 75% of the company's workforce is made up of union employees.

If the plan were to amend to allow employees from only the separate union agreement that includes the owner, would all union employees need to be included in the compliance testing, regardless if they are excluded from the plan? The concern is that including all union employees would more than likely result in failed coverage testing.

Treas. Reg. 1.410(b)-7

(B) Plan benefiting collectively bargained employees. If a plan benefits both collectively bargained employees and noncollectively bargained employees, the collectively bargained employees are one disaggregation population and the noncollectively bargained employees are another disaggregation population. If the population of collectively bargained employees includes employees covered under different collective bargaining agreements, the population of employees covered under each collective bargaining agreement is also a separate disaggregation population.