I'd assume that tumbling is possible while flying. To Frank's point, those are merely possible DC modifiers, rather than actual DCs (if you get my meaning). None of those modifiers would normally apply while tumbling through the air, except perhaps if one was flying through a forest canopy and dust cloud or a perhaps a swarm of fine creatures.
A similar question arose last session when I was lead to wonder whether it would be possible to make a jump skill check while flying. It might sound absurd, except that it's similarly possible to execute a counter-intuitive run action while flying.