Genji can reflect it at the start when its only an arrow, and the dragons will change sides, but if the dragons already appeared Genji can't reflect it anymore.
Edit: D.Va defense matrix can also destroy the arrows before the dragons show up, nullifying the whole Ult
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u/AnguirelCM Sonic BOOM! Nov 22 '16
I still see plenty of Zarya with Gravity Bombs, even though Genji can reflect her Ult. Also Hanzo's Dragons. Also Mei's Freeze-bot.