EMP weapons wouldn't set off detonators (in general). They would just fry any solid-state circuitry they contain without doing anything else - i.e., render a cell-phone detonator inert.
But I think the Israelis have built things like this... At least I've read an article or two to that effect. In other words, to send a pulse through a detonator and make it go off, the emp device doesn't have to be powerful enough to fry all the electronic contraptions around it. In effect, you're just tickling all the electronics in a given neighborhood, not frying them.