I think the Jem'Hadar never really needed Ketracel White to be loyal to the Founders. I think the Vorta were telling the Founders that the Jem'Hadar were not as loyal as they thought they were, so had them addicted.
The Jem'Hadar have shown themselves to be more loyal than the Vorta. For example, in "THE SHIP", the entire compliment of Jem'Hadar killed themselves because they failed in saving the dying Founder. The Vorta, didn't.
Keevan in "ROCKS AND SHOALS": he let himself be a prisoner rather than use the kill switch they are implanted with. The Jem'Hadar fought to thei dying breath rather than be sedated and taken prisoner.
I think the Vorta are overall less loyal than the Jem'Hadar.
I don't know why the founders even bothered with the Vortas and didn't just deal with the Jem'Hadar themselves