Plan has immediate entry for 401(k) but 1 year of service for the safe harbor match. 3 HCEs become eligible after the beginning of the year for the safe harbor match.
Question:
Is adp/acp testing performed with these hces included or because they became eligible for the safe harbor match during the plan year, are they deemed to satisfy the adp/acp safe harbor requirements?

why are you performing the ADP/ACP testing on a safe harbor plan?

because the safe harbor match is not provided to all "eligible" employees. Plan's coverage testing was run using permissive disaggregation and 3 hce's pop into the under age 21 / 1yos group.

An excellent question.

Remember that disaggregation for ADP/ACP should be consistent with the 410(b) test. This is true even if it is a Safe Harbor plan. So if you are using the end of the plan year for your 410(b) determination date, then the HCEs would NOT be otherwise excludable employees and their contributions would NOT be subject to ADP/ACP testing.

Not sure we have enough information here to answer the question(s), but I have a question: Are you sure you have new HCE's? Unless they are owners, I don't think they'll be HCE's until the second plan year.

Just a thought.