Awesome analysis. It sounds like accusations of firmware nerfing doesn't fit with the data. It sounds like they also shouldn't set to avoid empty blocks.
The explanation for ocean's high empty block rate is simple. They are sending empty blocks followed by a replacement (full) template with cleanjobs=false. However, some models of bitcoin Application Specific Integrated Circuits (ASICs) do not switch to this new work quickly, with cleanjobs=false. According to ocean's own data, some miners "will continue submitting the older work until they exhausted their search space which could be anywhere from 1 second up to a minute". This decision by the pool combined with the use of particular ASICs is likely the cause of their high empty block rate.