In this comment in mongodb/specifications#668, oleg.pudeyev referred to a recent SDAM spec change in
SPEC-1332. The text instructs drivers to populate pools for data-bearing server types; however, it does not address other server types (e.g. RSArbiter, RSGhost, RSOther).

jeff.yemin pointed out that there is little reason to create pools for arbiters, since they are only used for monitoring; however, it may make sense to permit drivers to populate pools for RSGhost and RSOther types, since those could become queryable nodes down the line. I propose "Connection Pool Creation" section of SDAM be amended to say:

• Drivers MUST NOT create connection pools for RSArbiter server types
• Drivers MAY create connection pools for RSGhost and RSOther server types

This would leave PossiblePrimary and Unknown as the only unspecified server types. I'm not sure if those bear mentioning, but if so I imagine we could add them to the list of MUST NOT alongside RSArbiter. Connection Pool Creation in the SDAM spec says the pools are only created after successful server checks, so perhaps that justifies omission of PossiblePrimary and Unknown (both types are transitive states before successful isMaster checks).