I'd like to use InnoDB on the master, for its transactional ability, but MyISAM on the slaves for the full-text search ability. Is this possible?
ALTER TABLE tblname ENGINE=MyISAM; against all tables on the Slave that you want to have the FULLTEXT index. Afterwards, you can run
ALTER TABLE tblname ADD FULLTEXT (column[,column]);.
Please be very careful not to run DDL against those tables in the Master that are unique to InnoDB that will replicate to the Slave.
I have suggested using a different Storage Engine on a Slave in my past posts: