We have a plan with an excluded class of employees, and it passes 410(b) - non-excludable members of the excluded class are considered non-benefitting.

Q: Are the otherwise non-excludable members of the excluded class included in the 401(a)(4) general test with a $0.00 allocation or are the omitted from the test? (EX: 10 participants + 2 EEs in excluded class, does 401(a)(4) cover 10 people or all 12 people?

they show up as 0's (in fact, even if they terminated with less than 500 hours, because that rule only applies to 'participants')
note, this logic is different from the ADP or ACP test where such bodies don't show up.