It seems the java.net.NetworkInterface implementation of android does not have a
byte[] getHardwareAddress() method http://developer.android.com/reference/java/net/NetworkInterface.html

I've found several forums of people trying to do this with no definitive answer, I need to get a somewhat cross-device UUID, so I can't rely on phone numbers or in ANDROID_ID (which can be overwritten and which I think depends on the user having a google account) http://developer.android.com/reference/android/provider/Settings.Secure.html#ANDROID_ID

In linux you can use ifconfig or read from /proc/net/arp and you can easily get the Hardware address.

Is there a file in android that I can read?

There has to be a way to get this address since it's shown in the "Settings > About Phone > Status" of the phone.