What about VIEW DEFINITION and being a member of the PUBLIC role?
Your best bet is to try viewing DDL triggers through SSMS with that account; if you can't do it there, you aren't going to be able to do it with SQL Data Compare I'm afraid and it comes down to it being a SQL Server permissions issue that you will need to resolve with your DBA and SQL Server Books Online.
The article I linked to previously though contains full details of all permissions required, so if you believe you've followed the instructions to the letter, as I said try looking at it in SSMS. If it is then working in SSMS but not SQL Data Compare, by all means let me know.
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