This would be a weird thing to implement. It'd work as its name implies - an iron door, but in fence gate form - but it'd have an additional quirk, as well. In addition to opening and closing with a lever like an iron door, it'd also stay open if pulsed by Redstone.
The reason I'd want such a fence gate in Nuismatics, rather than some other mod, is simple: It'd make a fare gate rather easy to set up given all the other equipment this mod already has. The pulse-open would make the door stay open when you pay a fare to the depositor, and the normal iron door behavior would allow you to exit with merely a pressure plate on the other side. you would find it difficult to jump the turnstile, as well, since it's a fence gate.