Well a few things....
Did the bowler/team know the person did not have enough games in? Did they know the league rules? The bowler may have known they only had X games in, but did not know they needed Y games in to bowl in the rolloffs.
However, it is up to the captain to know the rules, so no excuse there.
Further, if the league allows for pacers, not much you can do. Although it may seem disingenuous, remember that and make a point to bring this up during the meeting prior to league starting next season to change the rule moving forward. Or, if the league votes to keep the rule as is and allows pacers, you now know what can happen in the future.