This is nothing -> I
I don't see why not. Solaris is much like any other flavor of UNIX. Just compile & build Ruby from source and then run the Rails app. And after he gets it all up and running, a quick guide of maybe some platform-specific caveats would be helpful on the Wiki!
This guy came on IRC but I believe the answer was "install Linux" :p
"Install Linux" is not a good answer for Unix users, and they usually don't like it if they came asking for support on their platforms ;)
Solaris users can probably create packages from http://pkgbuild.sourceforge.net/spec-files-extra/ instead of building them manually.
Except that we require 1.9.2 or later, so that 1.8.7 one there won't work ;)