Generally, charity blackjack events turn pushes into wins for the casino. Real casinos do not offer such a hard-line rule, because players would never belly up to the table when the odds are so stacked against them. There is an exception: Double Exposure blackjack. Here, as compensation for losing in pushes, all dealer’s cards are dealt face up, However, (there’s always an “however”) because you get to view both of the dealer’s up-cards, the playing rules are adjusted to favor the casino more than in standard blackjack. It is a version of blackjack definitely worth avoiding.
However, regarding charity games that keep the pushes, and we are talking about a games deliberately designed to feed a buck or two into the community chest, the charity blackjack game that gobbles up pushes is simply part of the cost of philanthropic entertainment in support of worthy causes. But a charity blackjack game that keeps ties has an advantage of 8.8% over the player.