Implications are not RAW.
If characters can take mental stress from something disturbing they see in combat (and they can), then I see no reason why social stress cannot be taken as well.
Additionally, it makes sense to socially take out a character during combat.
Like, oh, "Luke, I am your father!".
Point for Bumblingbear.
Well, I was hoping not to jump into the whole RAW thing, but here we go:
"Social conflicts occur when the opposing agendas of two or more characters are resolved without physical violence, calling upon a different set of skills and trappings to resolve them. The damage done by these conflicts can be highly variable, ranging from simply instilling a false sense of security in the loser to ruining his public reputation and hurting his relationships."
Emphasis mine. If physical violence is involved, it's not a social conflict, and the application of social skills is best resolved via maneuver.
But, as you say, characters can take mental stress during combat, which seems to imply the same for social stress. However:
"Being able to attack the mental stress track is no small feat. The kind of abuse necessary to inflict this kind of damage on another person usually takes a great deal of time and energy .... Between mortals, some sort of prior connection or justification must exist to inflict mental stress and consequences."
Basically, to deal mental stress in a combat situation (well, to deal mental stress period), you need some sort of justification, aka a power that lets you do so. Incite Emotion, Dominate, spirit evocation (arguably) etc. deal mental stress because their descriptions explicitly allow them to. An Outsider that deals mental stress simply due to its frightening appearance should have the specifics of that ability statted out as a power, and that capability should be reflected in its refresh cost.
There are no analogous powers for dealing social stress at a moment's notice. I would argue that the RAW supports keeping social stress out of physical conflicts, although at the end of the day I think it's mainly about personal preference. Handle it however works best for your group.
As far as the climax of ESB is concerned, Vader didn't take Luke out in that fight - Luke's player totally went for the concession after taking the extreme consequence of "Severed Hand." If Vader had taken Luke out, he would have either captured Luke or killed him.