This is called security by obscurity. It works until it doesn't, and the guy happens to know how to work that system. Does it make you safer? Maybe. Is it worth your time doing this compared to other measures? Probably not.
It's probably safer to know how to secure Linux than to use a system you are not familiar with.
You are actually completely wrong. Those systems are significantly safer for two reasons:
1) they are (AIX & Solaris) or support (HP/UX with their PA/RISC emulation) big-endian binaries which for some strange but reproducible reasons seem to confound the vast majority of hackers/crackers and other mediocre programmers.
2) they are targeted for psychologically mature customers with stable requirements and not beholden to chasing most recent advance, change, regression, marketing trick of Microsoft, Google, and many others.
Definitely there's a component of obscurity in their safety, but it is a good obscurity, not a marketing euphemism for weak secrecy.
The true, large scale, hacking statistics are hard to come by. I believe the F5 Networks has the best statistics gathered through their application delivery appliances. But their keep it secret besides disclosing a little in their configuration examples how to remap the HTTP server names & fingerprints to trip up automated & scripted hacking tools.
