She wasn't necessarily ringed by the shota admiral or anything (or at least we have no indication of such), so no. Plus, (and perhaps more importantly) Robber-san hasn't made an intention of stealing her from anyone; she's just a girl that he fancies.
it's about stealing someone close and dear to NTR target, not necessarily lover, even sister, brother, daughter or a childhood friend are enough. So in that case admiral can be a NTR target.
Uhm, netorare to my knowledge only really refers to the act of stealing someone's significant other away from them. The words itself (寝取られ) literally means "taken away by sleeping with", which really wouldn't make sense if it can apply to familial loved ones in general. Otherwise, as an example marrying a girl would constitute NTR against that girl's father, which would be frankly stupid as that would mean every marriage in the world is NTR (unless said girl and her father were involved in an incestuous relationship).
For it to be NTR, the relationship between the two people being stolen from has to be romantic.
Hence considering the above, and the fact that the Admiral in this particular strip is a shota admiral, trying to label it as "NTR" would be beyond silly.
As for me it the overly-sexual depiction of the base.
I can't really bring myself to like it from the moral point, like those NTR and rape stuff.
The art style is fine but the content is... Maybe it's a different in culture issue.
For me I just wasn't comfortable with his pathetic admiral expecting everyone to be "pure" as he is. I mean anyone remember his asshole treatment of Maya? She was genuinely interested but he was a prick and she threw herself to another guy.
The rather overly sexual depiction was also a con for me. Granted it could be played for laughs with the right usage but it just comes off as a spiteful.
Now I'm not sure if this really reflects his view on women. He might as well be just trolling just to get heat. But we'll never know.
Personally I'm all for good old fashion vanilla romance and want to see if Robba-san will win over this shipgirl's heart.