Ok, just took a look at the requirements for taking a photo...
You need to have a target locked but other than that it does not matter if you are submerged or not. Also it works on the UZO, observation scope and the attack scope. So no real requirements there.
Took a screenie so you can see how everything looks...works perfectly btw.
The 'take photo' button is perfectly available even with the 'lock/break lock' buttons disabled.
Using version 1.5 and enhanced SH5 UI.