We can't actually tell you.
Two general points here. First, the SDK does not matter much. It's useful to work with the latest, but some stuff that is built in an old version 3 of the SDK doesn't generate anything significantly different from the same code built in 4.2. Or even built outside the SDK with your own maven installation and so-on. I think it's important to think of the SDK as a set of tools that make developing for Atlassian products easier than doing it all by hand.
Second is the Jira/Plugin compatibility. The answer to your first question is "it might be compatible", and the second is "no, a plugin does not contain several compatible versions". A plugin is built to match a specific version of Jira (or Confluence or Crowd etc). It MIGHT work for other versions, but it depends on what your plugin does, because if the APIs it uses to do things in Jira have changed, then it could well fall over. If, for example, your plugin has code in it that uses "user" objects and nothing else and you compile it for Jira 5.1, then there's a good chance that it will work on anything from 4.2 through to 6.0 because the user libraries are almost the same all the way through. It will fail miserably on 4.1 and below.
So, the short version of this answer is "maybe"
You must be a registered user to add a comment. If you've already registered, sign in. Otherwise, register and sign in.