Piscis,
The problem with any website is getting each and every one of your files uploaded to the web server.
I have not yet tried 3D instant website, but the only problem I can see is that SolidWorks might add an executable of some kind to the website. Most webservers do not run Windows, and many do not allow executables.
It is extremely unlikely that SolidWorks would do a dumb thing like this.
JHG