if i may clarify a little here...
a humbucker that's been put together from coils from 2 different pickups is usually referred to here as a hybrid.
these hybrids will usually (but not necessarily) have different gauges and/or types of wire on each coil, but as the coils will (most likely) not have the same number of turns on them, the pickup will (most likely) not be completely hum-cancelling.
dimarzio make dual-resonance humbuckers, which have 2 coils with different gauges of wire but the same number of turns; this forms the basis of the dual-resonance patent. you can tell which ones these are by checking the patent numbers for the different humbuckers on their web page.
some seymour duncan humbuckers have coils that are different (i'm fairly sure) in terms of the wind's exact number of turns, tension, pitch and pattern; i don't believe there are any SD pickups with 2 different types of wire (ie the coating) on one pickup.
as far as i can tell, pricing is a good indicator of which SDs are 'mis-matched' in this sense; my understanding is that the pearly gates is, and i suspect the screamin demon is as well due it's higher base price.