I don't think so.
I support another LARGE application using DB2 as back-end. but I am not the DF-Developer for this. Just the DBA.
They have plenty Indexes based on regular DB2 timestamps columns, and they never claimed about it, for more than 2 years. It's not possible to have this issue there for so long time and nobody noticed it.

The timestamps on DB2 are the same type, 6 milliseconds precision.