Fascism is not corporatist in any organic way. German fascism did not utilize corporatism until the end for instance. Given the pressures that system was under at that stage, I don't think we can attribute that to the normal function of the system.
Corporatism was linked to fascism based on Italy's use of it, but there is nothing about fascism that dictates corporatism be used. Germany proved this in the 1930's.
There's a few things which are of issue here.
The first is whether Nazi Germany can be used as an example of a "typical" fascist state, which it can't. I wouldn't go so far as to say its not fascist, but it certainly isn't typical of Fascism. For a start, from what I can gather, they inherently held the view that there was a definite divide between the people and the state - with the state being subservient to the "race", which is in direct contrast to the central fascist concept that the nation and the state are inseparable.
A comparison which I think would be reasonable to make is imagine them as being Socialism and Anarchism - at one point in time, they were essentially the same movement, but a time came when they diverged (I would perhaps suggest following the Munich Putsch?), much like at one point in time, Socialism and Anarchism were essentially the same movement, though they ultimately diverged as a result of (correct me if I'm wrong) the Paris Commune, and thus two different ideologies emerged.
The next issue is that Nazi Germany never adopted Corporatism. Ever. In their early days, prior to gaining any power, the Nazi Party adopted the policy of Corporatism, but this was quickly discarded when they felt that it did not fit in with their racially-oriented system, again, still before they had acquired any power. So it comes back to that they cannot really be considered "typically" Fascist - typical branches of Fascism would certainly fit around Corporatism ideologically. Though they could also substitute for other Third Way economic systems, such as Distributism, perhaps. In that sense, I'd suggest that Fascism is inherently Third Way, hostile to mainstream Capitalism and Marxism, and that Corporatism is generally the most "dominant" of the third way economic systems, so to speak.