If 401(k) plan requires ppts to be active on 12/31 to receive match...

Would this requirement also be applicable to participants who have reached normal retirement age (NRA) under the plan? That is, I know that participants must be 100% vested in employer contributions at NRA, but does that mean a participant who has reached NRA under this scenario would be 100% vested in the company match for the entire year even if they left before 12/31? Or would they only be eligible for the match accrued up until they left? (Match is deposited annually after year-end).

The document should outline if there are exceptions to the last day rule for retirement, death, and disability. 

Also, you seem to be asking about two different issues combined into one mashed question. One has to do with contribution allocation entitlement for the year of retirement - do they get or not get a match for that year? The other is a matter of ownership (vesting) with respect to their employer contribution account balances, are they entitled to 100% or only some lesser percentage?

As Bill noted, each of these should (must) be spelled out by the terms of the plan document.