To batch statements together for Oracle you need to have it enclosed in a BEGIN...END block. In your last example that you linked to in the comments you are missing a semicolon right after the second statement and before the END keyword.
BEGIN
CREATE TABLE TESTTABLE1
(
ID_TESTTABLE1 NUMBER (18) NOT NULL,
TESTTABLE_VALUE1 NUMBER (18),
TESTTABLE_KEY1 NUMBER (18)
);
CREATE TABLE TESTTABLE
(
ID_TESTTABLE NUMBER (18) NOT NULL,
TESTTABLE_VALUE NUMBER (18),
TESTTABLE_KEY NUMBER (18)
);
END;
Although FluentMigrator could provide better support in this case. For example, when FluentMigrator processes multi-statement scripts from Sql Server then it splits up the script and executes each statement (https://github.com/schambers/fluentmigrator/blob/master/src/FluentMigrator.Runner/Processors/SqlServer/SqlServerProcessor.cs#L197-236). So I would recommend logging an issue at https://github.com/schambers/fluentmigrator/issues