I have experience with Unix security going back to 1994, not as a job title but because my DBA / SE job always required admin access, plus I've set up company machines before and spent time configuring security. I will not touch your windows servers, someone else can better help you there.
However, I do not have blackhat "hacking into servers" experience as that is not what I do. So maybe you are looking for that specific type testing service?
If you want to talk more give me a PM.