Should I use "training in" or "training about"?

In most cases you should use training students in, but the answer isn't as definite as in this Stack Exchange question because of the presence of the direct object.

As an illustration, it is difficult to find the collocation training about, which suggests that it is an error. However, training students about ... occurs in fairly formal contexts. For example, note this newsletter entry by Megan Carlos, "Training clinical psychology students with disabilities in psychological testing and assessment." The title uses "training clinical psychology students with disabilities in" something. However, the use with about occurs in-text:

The range of anecdotal experiences described by trainees with disabilities, in combination with an absence of literature available on test examiners with disabilities, suggests that there is a lack of clarity among psychologists involved in training students about what constitutes reasonable accommodations for trainees with disabilities with regards to psychological testing in coursework, practicum placements and internships.

The uses are also mixed in an academic article, "Intimate Partner Violence in the Medical School Curriculum: Approaches and Lessons Learned." Training in appears first:

Not surprisingly, research has shown that physicians who receive specific training in IPV are more likely to screen for it ...

A few paragraphs later, training students about appears:

The patient population and the medical student body are among the most racially and ethnically diverse in the nation, which creates both opportunities and hurdles to training students about IPV.

From both of these examples, train(ing) ... about operates in a sense close to the verb inform(ing) ... about, where the object of the preposition denotes an information-based item: "what constitutes reasonable accommodations" and "IPV." A skill or a larger field of knowledge ("psychological testing," "IPV" as something physicians identify) would be less likely to follow training ... about, since about following verbs of conveying learning does not ordinarily do that. (I can't find examples of broader usage, which is a weak form of support but the best I have.) So training ... in has more versatility and can be used with a gerund like so:

"A Novel Approach to Training Students in Delivering Evidence-Based Obesity Treatment"

"Delivering evidence-based obesity treatment" is a larger skill, and 24,000 results in Google have the exact phrase "training students in delivering." As of this writing, no results exist for "training students about delivering," suggesting that the gerund (suggesting action or skill) may not agree with training ... about.

In overall usage, a very rough measure with Google search results suggests that "training students about" (with about 100,000 results) is ten times less likely to occur than "training students in" (with about 1,000,000 results). That also provides support for training students about being more specialized in use. It'd take a lot more research to fully describe what's going on here.

Finally, in your case, what you use depends on your precise intent. In the general case,

I have been actively involved in training students in Ground Operations,

there is no issue or restriction to think about. In the specific case,

I have been actively involved in training students about Ground Operations,

there are several factors to consider, and overall Ground Operations can only operate as a piece of information, not as a larger skill or field of practice. I would not use about if I were educating people in how to conduct ground operations, but I might use about if I were telling civilians or an elementary school class about what ground operations is.