Most likely red dog tags would be examined closely, as some of the Medical Alert Tags I have seen are red. Keep in mind the information that is needed in the field if you are found unconscious should be geared to significant medical information. Here is a brief list of information (others may have better ideas) in an order that I would consider important and useful, of course there is a limit to the amount of info that can be placed on a tag:

Name
Date of Birth (DOB)
Medical Conditions (diabetes, COPD, asthma, etc.) that are of significance in an emergency or may have contributed to your current emergency
Drug allergies
Medications
Other allergies (food/tree/grass/etc.)

While am I a sure, others can think of other info and level of importance, I feel the above list would be adequate. With huge lists of meds or those that have changing lists of meds, rather then having those engraved, perhaps an attached list in a small plastic vial or sleeve.

Information like:
Contact info
Doctors
Address
Phone numbers
Etc.

Are not really critical to treatment in the field, such info can be carried in your wallet, purse, notebook, etc. and would be helpful to law enforcement and the hospital.

Pete