Anyone know when utilizing cloud SQL MySQL if its possible to have one specific schema replicated to other cloud SQL instances?
As one of the option you can use https://cloud.google.com/sql/docs/mysql/replication/custom-import-replication-from-external but on the replication instance use replicate_do_db or replicate_do_table flags to replicate only what you need.
So could I have that external db/table import into existing cloud SQL instances?
Yes, I think so, using the standard mysql tools. It is the same MySQL after all as anywhere else.