Makes sense to me that this isn't something you do too publicly, agree (if nothing else, it's nothing to be proud about). There might be unofficial channels for these kinds of things, and as chief, you call on someone to set it up. There are multiple reasons to keep the Broos far away from your people, even when you call on them as mercenaries.
On the other hand, I don't think it needs to be kept completely secret - Praxians can be pragmatic, and a lot of them are likely to go "yes, this sure is distasteful, but what can you do?"