Short answer: Yes.
Long answer: I would rate Solaris on SPARC as one of the premium operating systems a sysadmin can work on. Others I would include in the same bracket are AIX and Red Hat.
One rung down the ladder but still perfectly respectable are HP-UX, Solaris on x64, SuSE and (God forbid) Oracle Linux.
Be careful about Debian, CentOS or Ubuntu. These are nice enough in themselves but not really suitable for enterprise use (which means most big companies won't care if you're experienced with them). I know some corporations do use these distros, because they don't need to pay maintenance or licensing costs, but I don't think it's a great idea not to have vendor support. In the event of a big outage you have no safety net.
Obscure Linux distros and defunct Unix versions should be avoided unless you're aiming to corner a niche. It is, however, worth spending a small proportion of your time working with The Great Satan (aka Windows), if only because so many UNIX/Linux roles do require some Windows work. Sad but true.