Many people are allergic to neem. I will use it in Veg as a last resort but I never spray at all once it goes into flower. DE is great for the floors, I'm hydro though so no need to dress plants with it. I have heard of people dusting the plants with it as well but again I wouldn't want to smoke weed dusted with DE any more than with Neem.
No doubt, I neem in veg and stop a week or 2 before flowering. I don't want anything touching the flowers but lots of air. =)
I've found being aggressive with protecting the plants in veg allows me to leave them alone during flower (in a perfect world).
In fact, I've ceased all outdoor gardening around the house just so I don't introduce any bugs to the room. Not worth the chance.
As a clarification, I would never dust the plants themselves with DE. I just top dress the soil itself.
At the end of the day, I'm growing for myself. I want my head stash to be as clean and high quality as I can make it.
As summer comes in, you can really see why Cuban Black Haze does so well in Florida indoors. It's like it's made for the climate. We've got high Temps and high humidity, neither of which bothers the black too much.