Are you talking about whitelisting an internal client or an advertising domain? If it's the former, the clients are just using Pi-hole as their DNS server; it's not something you need to whitelist. Have you tried whitelisting these Google domains?
There may be other domains to whitelist if you watch the query log when try to play some of those games.
Also, as you mentioned, you can just manually set the client's DNS to override them from using Pi-hole.