Looking at the wording of the rules i would say junk can be taken. Jink grants a cover save with no restrictions. Pg 26 for cover state that "models do not get cover saves from any wounds suffered from close combat attacks" That is the only restriction on taking cover saves. As vector strike is not a CC attack there is nothing that would disallow cover saves to be take.
As for the grounding test again we must look at the wording.
"if a flying monstrous creature that is swooping suffers one or more hits from a units shooting attack, it must take a grounding test immediately after that shooting attack has been resolved"
Specifically states "shooting attack". As vector strike is not a shooting attack i would say no grounding test.
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