If they are made in the USA, then yes.
More specifically, the number of imported parts needs to be 10 or less ... according to Mr M4Madness's ATF letter, the m4 is made up of 11 imported parts. Replace one of those imported parts with a US made part, and you are fully legal.
Now, I don't think there have been any cases of this being enforced/upheld, so it is all theory right now.
[ 07-07-2006, 06:23 PM: Message edited by: Duggan ]