I won't speak to specific examples, but I will say that it's so prevalent that Canada Revenue Agency has a charities directorate that deals specifically with terrorist financing. It screens the principals in every charitable organization in the country against watch-lists and lists of known nefarious individuals. It is a commonly known method.
Part of the reason is the difficulty for any institution, reporting entities included, to evaluate what's normal for a charity. Donations go up and down. Donations can be cash. Evaluating what the baseline is and distinguishing good dollars from bad dollars is very difficult in that context.