You could hammer it flat _and_ find a thin steel washer that fits the head of the nipple. No regular tension nor wear and tear would be able to pull that through the rim.

The reality is that it would not be dangerous to have a spoke blow on you (been there, got startled, wrapped the dead spoke around the next one so I could limp home, I take that over a blow up flat any day) but it is potentially a huge waste of time; you build a wheel that you end up having to scrape.