Unless I'm not reading an accurate copy (
http://usinfo.state.gov/usa/infousa/...w/civilr19.htm) I don't find "culture" mentioned in the Act.
Even if dreadlocks could be called a Religious Expression, then it would still depend on how the court rules when someone sues over it... so until someone sues (and there is precedent) then employers can prohibit stuff like that if they wish.
(I have no experience in such matters, but am an employer. This is just my take on it from what I've read and heard over the discrimination issue)