Why would they need to take by force something they can make?
Why would
they need to take by force something that they already have? The very point of the arrangement is that the Vorta have the White, and thus have direct power over the Jem'Hadar who otherwise would pay no heed to the Vorta (even though they worship abstractions like the Mission and the Duty and the Founders, and thus never disobey anyway).
Somebody needs to make the White. In order to do so, they need to know how to make it. The recipe obviously is a well-kept secret, and there are ways of keeping recipes secret even against rampaging hordes who can trivially capture all your cooks and torture them for their information. We already see some examples of this, with the portable safes that the Vorta use to stop the Jem'Hadar from getting White at will (no doubt the safes are engineered to destroy the White if anybody but an authorized and willing Vorta tries to open them, plus to make it difficult for even one of those Vorta to open them for selfish purposes such as self-survival).
No such arrangement is perfect, though: there are always ways for a few Jem'Hadar to get their dirty hands on a little White. But in the bigger scheme of things, that doesn't matter: such rebels are mercilessly mowed down by loyal Jem'Hadar, as in "To the Death". There's no constant rebellion bubbling under the surface of perfect slavery - there's willingness to obey, and deep disgust at the thought of betrayal. After all, the Jem'Hadar know they are on the winning side...
Well, certainly not THAT way! If only X knows how to do it, and X
doesn't do it, it doesn't get done. Simple as that.
There must be cooks out there with the recipe. We know the Son'a are such cooks. They aren't specified as being unique. The Founders just employ them, and other cooks, much like they employ folks who clone Jem'Hadar and Vorta, and folks who build weapons. We have seen how the weapons come from the Karemma ("Starship Down"), and the fact that a subjugated species builds them is clearly not a risk to the Dominion. Heck, the Nazis trusted the building of their most powerful superweapons on the people who hated the Nazis the most (which admittedly meant the work was shoddy, but that just goes to show the Nazis were too soft by Founder standards).
Timo Saloniemi