In my opinion it could still be the Drakh. Remember, in 2265 G'kar has never seen a Drakh as far as we know. And the Minbari only encountered them once, in 'Lines of communication'.
And if I remember Crusade's episode War Zone correctly, ISN said earth has been attacked by an unknown alien race. Gideon said they only knew a name, the Drakh.
So the Drakh are still an unknow race to the people, and perhaps to the minbari people too.
<table bgcolor=black><tr><td bgcolor=black><font size=1 color=white>Spoiler:</font></td></tr><tr><td><font size=2 color=black>
The archeological dig mentioned in the trailer could be the dig by the Drakh to an ancient Shadow base, as described in the Centrauri Prime trilogy book 2. It's a guess, I don't know if the dates match. Dates giving in the CP books are inacurate, so they don't rule out this option</font></td></tr></table>
------------------
"I don't watch TV. It’s a cultural wasteland filled with inappropriate metaphors and an unrealistic portrayal of life created by the liberal media-elite."