English translation: assist, back up, support, receive input from
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Explanation: As you already said:
"Does that mean the Mitarbeiter assisted the instructors or acted in an advisory capacity or maybe even taught some courses?" - It can actually mean all of this. "Begleiten" alone is not sharp and clear enough to qualify the activities. At first look I would say they also have taught at that facility.
So if your context does not give you any more hints of the capacity, these people are working in, "assist", "back-up" or "support" would be best to use.
Thanks, Hans-Henning, and everybody else for good suggestions. The translation is gone and I weaseled my way out by saying that numerous staff members "were involved" in the courses, since it was not clear what they actually did :-))