Generally speaking, yes, of course! At least I've never seen any "no windoze lusers please" in Unix-related jobs postings :-)
However, I would recommend you to get at least a year of experience (half a year as a bare minimum) of Unix development. For that, simply install some Linux distro (Ubuntu or CentOS for example) and play with it for a while to learn the libraries and APIs. As you are an experienced programmer, it shouldn't be hard for you to learn another technology stack.
So, just play for a while with the things that you want to develop for money, which may be networking programming, GUIs or anything else.
Another option is to take a look at some of modern cross-platform stacks, like Java, Ruby or Python.
Hope this helps :-)