Ipstenu (Mika Epstein) on "Can I convert all tables from MyISAM to InnoDB?"

WordPress actually specifies no table type in the create statements, so it uses MySQL's default table engine which is InnoDB from version 5.5 onwards.

Which is to say if you changed your DB on the server, it would do this.

https://dba.stackexchange.com/questions/58998/myisam-with-innodb-in-the-same-wordpress-database-reduce-performace