We just added two 2012 servers to our 2003 domain and added the DC roles. In Sites and Services Console all servers say they are Global Catalogs "GC" and none "DC". We did the same exact thing at another location and one of the 4 servers is listed as a DC. The two locations are not connected BTW, I am just stating this for comparison.
We are planning to remove the 2003 DCs soon but we are not sure is this will cause a problem or why there is a difference.
Image is attached.