Hi Anthony,
As my article is only a technical view on the system I would recommend the following for real world usage.
The influence on the metering system would only be noticeable at all when the focus light represents a large amount or all of the ambient light. That means you really can ignore this item underwater. It might be noticeable on a night dive when distance is just a few centimetres. But even then I would expect the results not being completely out of range.
As far as I remember the diffusers are identical to my Z220 ones and have a hole for not blocking the focus light. So if you really feel the need, I would try the recommended filters by Inon.
I think it was mentioned somewhere that your Fuji camera does not emit a preflash. That would mean the Fuji has an external sensor for flash exposure metering? In this case you don’t have to care about the filters at all as there is no preflash influence.
As far as I remember you might have to insert the magnet screw in your case in order to disable the D2000’s preflash handling. And maybe switch back to external auto strobe function. But this depends if your Fuji really emits only one mainflash and uses an external sensor. The external camera sensor might not deliver reliable results due to blocking from the underwater housing.
If you have detailed information on your Fuji’s strobe method it would be easier to figure out which mode to use.
Regards,
Julian