Legality has zero to do with employer policy enforcement and isn't an applicable argument. You can argue it, but it wont hold water. To AG's point a judge has yet to rule on whether he was guilty of a crime or that the search was legal.

Texas has no motorcycle helmet law other than having to have sufficient insurance to ride without one, employers are perfectly within their right to require a helmet while riding on company property.

Open and conceal carry are legal in Texas with a permit, business owners and employers are within their legal right to post a sign forbidding either carry on their property.

Long hair and beards are legal in all 50 states, not if you are employed by a branch of the US military unless job description allows (special forces, etc...).

There are too many examples of how something being legal doesn't effect an employers ability to set and enforce policy against it.