Well...
Actually both cartridges use bullet diameters of .355", so the chamber throat, forcing cone and bore won't present any problems.
If the revolver uses the rim of the cartridge, like my S&W 547, or a moon clip, like my Ruger SP-101, to establish head-space, the .380 will not enter the chamber any farther than a 9mm so that shouldn't be a problem.
The case of the 9mm is, very slightly, tapered and so the rear-most part of the .380 case might bulge slightly, possibly even rupture though the chances are poor. Sticky extraction is a better bet.
To answer your question: The .380 is most likely "usuable" in a 9mm revolver but not advisable.