Is there a standard way to track PUE for Liquid Cooled Workloads?

Liquid-cooled products each DC operator offers are still in a very early concept stage. Adopting a certain way of measuring and reporting liquid-cooled PUE is difficult, so it is likely to be very crude as you explained. 

PUE varies by liquid solution type, and several key parameters are at play that determine it. The first one that you mentioned is whether the server fans are accounted for in the IT load, 100% for air-only cooled IT, ~10-20% for DLC, and 0% for immersion. The industry never tracked the server fan power component in the past, so it is not something you can deduct to get accurate like-for-like reporting. 

Then normally DLC cooling has Cooling Distribution Units that contain the pumps and liquid-to-liquid heat exchangers. There is a question as to who owns the CDU, if it is the operator, it could be easier to add it to the non-IT power PUE component whilst the opposite could be true if it is a custom-made liquid cooling solution and the Customer brought in their own CDU. 

There is another liquid-cooled DLC solution which has a liquid-to-air heat exchanger rejecting heat in the data hall, and then you have CRAH/CRACs to take it out, it is a rather weird and inefficient one, but it exists. This is more likely to have onboard pumps that are included as part of the IT load.

Also, the liquid cooling SLA temperatures will determine whether you'd need to connect your CDU to the chilled water loop or preferably directly to the condenser water loop.

All of these nuances in the solutions add complexity to the PUE reporting, and if these solutions are in a shared data center it is likely that some blended PUE metric has to be developed as a chargeback model and simple admin process, or you'd have to track two PUEs - one for air and one for liquid. The liquid one excludes power contribution by some components such as CRAHs, Sec. Pumps, Chillers, Mech UPS based on the case scenario.

I have attached an example TCO calc from one of the DLC liquid cooling vendors with the liquid-to-liquid HX in the CDU. If you are curious, you can see how they calculated the blended PUE for their equipment and the parameters they assumed. You should take it with a grain of salt because the person who developed it is not very familiar with the DC Colo industry. I also think the revenue they demo off for liquid cooling vs air cooling is off.

I trust this stirs up some good