Hidden replica set members may not be considered as part of write concern calculations. Recipient nodes should never be considered in write concern calculations, because they can't guarantee they will keep the data they would be promising to persist. We should do the following:

• update our "steps for cloud" to indicate that recipient nodes should be configured into the donor with the hidden: true key (see more detail in the linked document above)
• update our validation to ensure that recipient nodes have the hidden: true flag before starting a shard split operation
• update tests and test infrastructure to accommodate this change