If i go to https://addons.opera.com/extensions/ using Opera 12 i can see lots of them.
I'm after Ghostery-0.10.0
Well don't i look foolish, thank you for confirming it's possible.
Even though "Identify as Opera" is selected as default, it was still identifying as firefox
So many google searches came up with "now opera12 extensions aren't available" etc i believed it was the case.