I don't know of any major difference between Oracle Solaris ou Oracle Linux, besides those that are operating system and hardware specifics ( Oracle doesn't support Solaris x86, so besides the OS, there's a huge difference in hardware too )... Personally, I choose Solaris or HP/UX for a Oracle DB...
First you got to ask yourself some questions before choosing one operating system or another that will fit your needs...
Check this document
http://www.interealm.com/technotes/roby/pentmark.html , it "talks" about Oracle on linux and Oracle on windows ( same hardware ), below there's a table where Oracle for Solaris and HP/UX are mentioned as well...
In the meantime, if somebody has a different answer...