In monCachedObject the ObjectName column actually contains the name of the table (if indid=0) or the index (if indid>0).
I don't have a copy of any monDeadLock records in front of me so my first question would be ... does monDeadlock.Objname serve double duty holding table and index names (like with monCachedObject)?
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As for 'is the indid hidden in ... monDeadLock'? *shrug* I'd have to do the same thing you've probably already done ... pull the records from monDeadLock and look at the contents of each column to see if any of the data looks like an indid/index-name/partition-name/or-anything-else-that-could-tie-back-to-an-index.
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Another idea ...
Since you've stated you can see the index in the dataserver errorlog ... have you thought about enabling monErrorLog? Granted, you'd have to parse the textual data in the ErrorMessage column, and then there's the question of how big to make the monErrorLog pipe (depends on volume of activity and how quickly/slowly you get to the data in monErrorLog).