Which type of repair level is “DBCC CHECKDB (databasename, repair)”?
Running this on a sufficiently corrupted database results in the following error message:

Msg 7909, Level 20, State 1, Line 1
The emergency-mode repair failed.You must restore from backup.

This leads me to estimate that REPAIR is simply the short form of REPAIR_ALLOW_DATA_LOSS.  In the very least, I would treat it as the same when it comes to expectations around recoverability of the database in question.  In other words, this should be considered the operation of last resort, only to be tried when all else fails.  Make sure you make a physical copy of the database before running this process.