If the tube goes into the bloodstream, the Jem'Hadar must have very robust hearts! A human heart would seize immediately at receiving such a barrage of giant air bubbles...
But that's the point: the dead man's switch is necessary in case the loyalty gets misplaced. After all, the Jem'Hadar on the field have no cues as to what the Founders want of them, and can develop dangerous ideas either all on their own (they are capable of independent thought, but are aggressive idiots by philosophy) or because their immediate masters don't serve the best interests of the Founders unquestionably (as is often confirmed).One thing you can usually depend on in an army is loyalty to whoever they are fighting for.
The average Jem'Hadar won't have seen a Founder, ever. He doesn't know who he is fighting for, he only believes he does.
In any case, the loyalty of an army to you is hardly something you can depend on, unless you pay them well enough. You might depend on them being loyal to a cause you have propagated into their thoughts (say, protect the homes and the apple pies), but even then it's not uncommon for the army in the field to decide that the best way to do that is to ignore your orders because the cause alone suffices for leadership.
Timo Saloniemi
I hate to bring up SG-1 again but from what the Vorta say on several occasions, the Dominion are gods to the Jem Hadar as well as to the Vorta. That would have been bred into them in the same way it was bred into the Vorta. It is explicit, in the same way as the Goauld control the Jafa by making believe they are gods. No other control is needed once you have that kind of obedience (the standard brutality for transgressors will suffice).