You can use the Valve Source ModTool addon with the commerical version of Softimage, but if you are using 64-bit Softimage, none of the compiled Valve Source plugins will be available (because they’re all 32-bit).

So, that means no SMD, Weight, or VMF import and export in 64-bit Softimage. You can use install 32-bit Softimage if you need access to these tools; 32-bit Softimage will run with the same license as 64-bit Softimage.