Radial / low flange - safe?

Yep, Shimano didn't warrant all their hubs if laced up radially (until a couple of years ago).
I had several (front) hubs with radial spokes, never a problem. Appearantly Shimano had enough claims to state that it was not allowed.

current (36 h not sure about the 32) Dura Ace track hubs come with a little note saying "don't fucking radially lace this hub, you hipsters"

despite this, people continue to do so, without any problems. Personally though I would obey the manufacturers.
I have a radially laced front (to an on-one/halo type hub shell) and my other wheels all 3x, there's no fucking difference really, except I feel safer with 3x tied and soldered on the track because they wheel will stay together in a crash.