I researched this topic and found a couple mentions on here that the EFX helmet had been approved for the 501st. I reached out to a GML with my local 501st garrison and asked directly. I was told this, but I guess it depends on the GML and garrison that you ask:
"The EFX, in a word... no..... the biggest problem is EFX decided to put these exaggerated grease stains all over it, which are heavy handed, (ie like a child did it) and they’re not present during ESB filming. The stains that are on the helmet now are post production as they haven’t treated it well in the following years. In the BHG, we’ve had command staff discussions about it, and the other issue Is the seam on the dome, which is obvious."