Generally, yes the BT standards are adhered to and are backward compatible with all current versions of the BT profile versions however, that's not always the case with headset compatibility with various devices. Some headsets just don't work well with iOS period. In my profession, it's like the world of "HDMI" connectivity with audio/video and the issues never end. Even though there are similar standards required with the HDMI profiles versions.
Personally, I've never had much luck with any "stereo" BT headphones on iOS anyways, regardless of the version. Unless I'm in a confined environment, they always seem to disconnect, break up and are choppy. I think the technology is still weak, in its infancy in that arena and will get better over time. I have the Sony MW-600, amongst others, it's a great BT module, but over time it develops connectivity issues, mostly with phone calls. It might work fine with Sony Ericsson mobile phones (which really that's what Sony designs their headphones for) but not so much with Apple iOS. Any of the mono BT v3.0 headsets I've used, pair & connect fast and seem to work well with iOS for me.