From my read, Greg Cochrane worked for Uranium One when Mitsui...

From my read, Greg Cochrane worked for Uranium One when Mitsui bought into them ... not directly for Mitsui.

Besides, uranium is not in the same Business Unit as fertilisers or salt at Mitsui (uranium is in The Energy Business Unit, fertilizer is in the Nutrition & Agriculture Business & salt is in the Basic Materials Business Unit), so the chances of Cochrane having any 'relationship' with anyone of substance in the salt or fertilizer business units at Mitsui are close enough to zero.

This is not to say that Mitsui couldn't be a potential partner for RWD, in fact they have looked at RWD at least once in the past & have to date not proceeded .... my guess is that the project was too early in the development stage to purchase outright & that the RWD corporate culture would not have worked for Mitsui as a JV.
I believe that if Mitsui were to move on RWD it would not be until all uncertainty regarding resource & production were removed.
Alternatively, they could take an off-take position (which could easily absorb 100% of production regardless of the size) but that would be unlikely until the production process has been franked ie until the BFS sees light of day.

However, companies the size of Mitsui are not interested in getting into bed with businesses run by demonstrably underperforming, slow moving, can't shift with a blow-torch, management .... no matter how good the resource, so my guess is that Mitsui would only be interested in RWD as an outright purchase & that wouldn't even be a consideration until all production uncertainty had been extinguished & even then, 400,000tpa may not be big enough for them ..... the WA salt business ships nearly 10 times that pa