DB2 on z/OS is not officially supported so this issue won't taken any further at this stage.
See: http://confluence.atlassian.com/display/DOC/List+Of+Supported+Databases

I have attached the two DDL's that are reported to work around the z/OS incompatibilities.

These two sql scripts are untested and are not supported in any way. Atlassian does not have the hardware to validate or test these scripts. They are use at your own risk.

I was able to get Confluence working with DB2 for z/OS as an external database with sample database created on both DB2 for z/OS V8 and DB2 9 for z/OS.
I had to create the objects myself, use the "unsupported database" option. I did not specify any hibernate dialog.
Confluence finds the tables, and I choose "overwrite existing data".

I have sent the DDL used via e-mail.

Regards,
Pat

Foriegn key DDL incomplete for DB2 for z/OS.
When creating foreign keys, need to specify ON DELETE CASCADE or ON DELETE NO ACTION.

[hibernate.tool.hbm2ddl.SchemaExport] execute Unsuccessful:
alter table ATTACHMENTS add constraint FK54475F9017D4A070
foreign key (PREVVER) references ATTACHMENTS
– url: /setup/setupstandarddb.action | userName: anonymous | action: setupstandarddb | referrer: http://localhost:8080/setup/setupstandarddb-start.action?database=db2
2008-03-21 11:53:03,266 ERROR [http-8080-Processor4] [hibernate.tool.hbm2ddl.SchemaExport] execute DB2 SQL error: SQLCODE: -633, SQLSTATE: 42915, SQLERRMC: CASCADE OR NO ACTION

As I mentioned in my e-mail, the next level of error after BIGINT gets resolved is the NOT LOGGED COMPACT column specification.
I've reproduced this problem connecting confluence to DB2 9 for z/OS (where BIGINT is supported).

SQLCODE: -199, SQLSTATE: 42601, SQLERRMC: LOGGED;NULL
– url: /setup/setupstandarddb.action | userName: anonymous | action: setupstandarddb | referrer: http://localhost:8080/setup/setupstandarddb-start.action?database=db2
2008-03-21 11:52:44,199 ERROR [http-8080-Processor4] [hibernate.tool.hbm2ddl.SchemaExport] execute Unsuccessful: create table PLUGINDATA (PLUGINDATAID bigint not null, PLUGINKEY varchar(255) not null unique, FILENAME varchar(255) not null unique,

Information about what JBOSS did to work with DB2 on z/OS:

• http://wiki.jboss.org/wiki/Wiki.jsp?page=JbpmOnDB2

DECIMAL(19,0) has been used as a substitute for BIGINT in DB2 for z/OS V8.

DB2 9 for z/OS supports BIGINT data type.