Interspersed Outburst & Ancient Dragons (spoiler? )

I heard that if the dragons get slagged while in midair, they will be resistant when they land.
First off, is this correct?
Would it defeat the purpose of using a non-elemental weapon while they are airborn
if I have Interspersed Outburst ?
I love the Slagga but don’t know if it would be of use here.