That is an interesting precedent. However, Ukraine is not a breakaway state from an existing EU member state (or a state which has been in the EU). There are numerous regions in the EU on a similar path, and none have yet succeeded (including Kosovo, which has been independent since 2008).

I'm also not talking about the defence of Scotland itself, I'm noting that monitoring and curtailing Russian naval activity in the Baltic Sea corridor is of wider strategic importance. If Scotland became unable to do this, Russia would have an easy exit path for naval vessels from its Baltic Sea ports.

In your example, Ireland as an EU member has significantly more access to military resources than otherwise.