The ability to JOIN on an OR clause in Tableau is currently a feature request. Please vote up the idea in the Tableau Community forums: https://community.tableau.com/ideas/3735
Additinoally if this is being performed in a Custom SQL connection. Please test Tableau Desktop and the Custom SQL query by performing the following steps.
1. Obtain the query in question to be tested against the data source outside of Tableau Desktop with the SELECT (*) wrapper as listed below.
The query Tableau Desktop usually sends looks like this:
SELECT Test_SQL.* FROM
( CUSTOMER'S CUSTOM SQL ) Test_SQL
Be sure to include the ().
Does the query complete successfully? If so there might be something occurring with Tableau Desktop when attempting to executre the query. Please also include any error messages that occur while attempting the join.
Hope this helps!