One of the assumptions is safe: low oxygen environment. This bacterium does not "eat" metallic iron, but reduces dissolved iron oxide which requires a reducing (I.E. anaerobic) environment. How the existing iron structure turns into iron oxide is another question. My brief poking around on the internet (I'm not going to call it research) seems to indicate that these bacteria live in conjunction with many other bacteria and fungi in an associated called a
rusticle which only seems to form on wrought iron. Modern steel should not be affected by this particular association, and chances are anything exposed to open seawater probably would be naturally exposed to all of the component organisms needed. Weaponizing this phenomenon would probably end up being more like developing some sort of fertilizing agent that hastens the colonization and growth rate of the appropriate colonies of organisms and would likely either be so bulky as to be noticed during routine maintenance, or require multiple reapplications which would increase the likelihood of being discovered. I really don't foresee this being more effective than traditional sabotage methods.
Researching this phenomenon is probably far more likely to give us a more thorough understanding of oxidation and improvements in the rust resistance of steel.
Who knows... the whole thing seems to be speculation at this point. After a bit of digging I think I found the paper that is being referenced
here. It looks like they isolated some organism and figured out its taxonomy using molecular techniques and very little research on the bacteria's actual metabolism. For all I know this particular bacteria could be simply feeding on those that are doing the actual oxidation and reduction. It looks like I'd be able to learn a bit more on the topic of bacterial mediated corrosion
from this document. Maybe I'll have that digested by the time this article comes up as a dupe.