yes it is allowable.
The restriction is that a recess appointee then has to be confirmed by the Senate by the end of that Senate session, otherwise the judgeship expires.
So even if a recess appointment happened somehow, Kavanaugh would still have to be confirmed at a future date, in order to stay on the Supreme Court.
Well that could be up to 2 years and if the mid term elections go Trump’s way.......
And we all know the left will use any delay they can.