Yes, but the corporation there is trade unions, guilds, etc not particularly business. Moreover the "merger" is not some mere overlap but complete union.

https://en.m.wikipedia.org/wiki/Corporatism

https://en.m.wikipedia.org/wiki/Corporation_(feudal_Europe)

I think it's somewhat defensible to label "fascist" cases in which business corporations in particular have outsized influence on the State, but that's not what Mussolini was describing.

His notion of the corporate state is corporative - an embodiment. The State itself is made up of the bodies or organs of society. It ceases to be a truly separate institution. As Mussolini famously said: "All within the state, nothing outside the state, nothing against the state."

It is not that institution A (say, Boeing Aerospace) has a lot of influence on institution B (US Federal Government). They are to be really merged, to be indistinguishable in some real sense.