Hurdling is also over something in front of you. I think if you jump/dive into a scenario where the head is already there then you've made it potentially dangerous. May jumped into clear space.
There's various wonder try clips on YouTube, a few similar to the May try, one indeed (Australian I think) ended with the jumper's foot landing on top of the would be tackler's head (who had come from side, as per May scenario). Nothing was said or done there either.
I've been surprised by the attention this try/action has attracted. Had May jumped a tackler in front of him, I'd have a different view.