Does chromium oxide form on Stainless-steel in 'deoxygenated' water?
From a practical standpoint, once the stainless steel item is made the passive layer immediately begins to form. Passivation with acids is a process used to accelerate this process and have parts ready to use in a shorter period of time. So if you have any high quality SS parts, they will come to you with the passive layer already developed. 

Theoretically speaking, if a completely naked section of stainless was put into this "pure water", there would still be some oxide formation because the specification of &lt;50 ppb still allows for some oxygen to be present. However, this should not have any practical implications. I suspect the name "deoxygenated water" is used to indicate there was a conscious process used to reach such a low amount of free oxygen in the water but not to claim o% free oxygen content.