Menach and Gary, Hi....
As happens too, too often with Wikipedia, the information given at that link is not fully accurate. In fact, if ever I saw or was served za'atar that looked like that in the illustration, I would either have an apoplectic fit or go to a good attorney. Whole pine nuts in za'atar!!!! Ye gods....not even under pain of death!
I do exaggerate a bit I know but at any rate - Whether the original za'atar was hyssop, wild oregano or wild thyme is a major source of debate for food historians, but agreement in general is that the Biblical hyssop or za'atar referred to in both the Old and New Testaments was origanum syriacum, which is demonstrably a form of hyssop.
Interestingly, za'atar plays a very important role in the history of what today we think of as fast food. Nearly 4,500 years ago, vendors in open markets in Sumaria would set up stalls at which they sold both ready-to-eat foods and foods to prepare at home. As hungry people made their way through the winding streets of cities such as Ur, they would often stop to snack on meat kebabs, stuffed vegetables, fried or boiled chickpeas, and various forms of kubbeh, nearly all of which had been seasoned with za'atar. And, as a spice (even though actually an herb), za'atar was the regional favorite for at least four thousand years.
Wild hyssop continues to grow in Israel and in parts of Palestine, Lebanon and Syria but in all of those places the plant has been declared an endangered species and picking it is forbidden. Despite that prohibition, wild hyssop can be found rather easily in the various Bedouin markets in any of those countries as well as in the shuks of many cities so long as you know the owner of the shop well enough.
Most of the za'atar purchased these days is actually a blend of various herbs and spices, those most often including wild thyme, wild oregano, sumac, salt, ground sesame seeds, ground coriander and black pepper. If I had to recommend one as the very best that would be the za'atar produced by Spices by Elena, an Israeli based company exporting to some of the finest food stores in Europe, the UK and North America.
As to the use of za'atar.....sprinkled over humous as you say and in many other ways. Pita bread, toasted, spread with olive oil and then sprinkled over with za'atar is a marvelous treat. Also commonly used, but in moderation as its flavor can be rather dominant, with grilled fish, roasted or fried lamb or mutton, grilled chicken.....