I'm sure it is not supported. Episerver would get very confused with two code bases and one database. I would keep the sites in one solution and implement some template selection logic if you need different model/view/controller for each site. It is also possible to create a custom ContentTypeAvailabilityService to filter content types based on current site. See more details about that here: http://getadigital.com/no/blogg/controlling-content-type-and-property-availability-in-multi-site-solutions/.
Either that or use separate databases and find other ways to share content if you still need to have different solutions.
OK, thanks. It seems Ektron is unique in this regard (at least as far as the other .NET-based CMSes I've researched).
We would like to set up a multisite so that our websites can share some content (same database) but use different Visual Studio solutions for each website and different IIS sites for each website. Is this possible?
Note: I read http://world.episerver.com/documentation/Items/Developers-Guide/EPiServer-CMS/7/Deployment/Configuring-a-Multi-Site-Setup/ but wasn't sure what "same files" meant. I assume it means that one Visual Studio solution is used for all websites and am hoping that is only a suggestion. :)