Looks good overall - this is definitely a useful tool to have. I'm posting comments so far but I will come back to it tomorrow to finish up.
So what would be the recommended procedure when the tool reports an inconsistency? Would operations have to go in, stop the brokers and truncate the log segments to the last segments that are verified to be consistent? If so, it would be convenient if the tool could issue another OffsetRequest to report the offset boundaries of the last consistent segments so you don't have to work too hard to determine the segment file.
Also, unless I'm reading it incorrect additional caveats are that the tool can only keep working so long as: partitions are not being added (or reassigned); logs are not being compacted.