Such pacts are probably also a standard way for the Dominion to operate when expanding its territories. The less direct conquering with guns they have to do, the better: the Jem'Hadar are an "army in being", a threat that is at its greatest when it is absent. That's why they are invisible, too - they can't actually fight when invisible, but one has to fear them all the time because not
seeing them is no proof that they wouldn't be listening...
Treaties, veiled threats and deliberate withholding of force - these are the two favorite weapons of the Dominion.