You might think obscured_oral should imply obscured_sex, but there's a couple of problems with that. For starters, obscured_oral could perhaps someday be used to tag obscured_masturbation such as obscured_autofellatio, though there are currently no instances of that tagged.

Furthermore, there's an obscured vs. offscreen distinction for sex:
^{(I'm using oral examples, since it's relevant to the discussion)}

Obscured_sex:
Sexual contact is within the frame of the picture, but obscured from view (usually by a body part, like a head or foot):
post #32910 post #3516357

Offscreen_sex:
Sexual contact is obscured by being outside of the frame of the picture
post #3057652

This distinction does not exist for masturbation. Obscured_masturbation is used for both.

So, even if obscured_oral is limited to sex, assuming it's like obscured_masturbation in that there's no obscured vs. offscreen distinction, we can't imply obscured_sex, since it could be offscreen_sex.