No, you can't do "includes" but you can put things into named objects.
For example, take your Tab #1 file, put it in a file called "Tab1" (or a better name that relates to what it's actually displaying; I don't know so can't help you with a name).
So in Tab1.qml we have:
import ...
Tab {
id: tab1
...
}
And then in the main file you can now reference it:
...
Tabview {
id: frame
Tab1 { id: tab1 }
}
You'll note that I included an id for it again, as the parent won't be able to reference the id within the child without it. (they can be different names, but don't do that. Animals will cry. Actually, you can leave out the id in the child as well, but many people like being able to see it within a file.)