Let's see.. few things I know about the EA-Narn relations..
First of all, the Centauri were the first race to contact the humans. Even with the first contact with the Minbari, the Earthers, already knew who they were facing. They had at least heard of them. I don't think it can be considered canon that the Earthers do not know who the Narn are.
The Centauri kept the closest ties with the Earthers up to the Earth-Minbari War. It's at that point that Narn and EA relations start to warm up with the Narns willing to sell high end weapontechnology, while the Centauri did not want to cross the Minbari. I do believe they gave some sort of support, which basically focussed on allowing some Earthers survive the war, but they did not trade weapons, which the Earthers wanted.
But before that, I imagine the Earthers were well warned by any race, because it's the period where the Narn were establishing themselves as a major power, a race of conquerors. They were actually pretty unpopular.
Other than that, there undoubtedly was a first contact between the two at some point. But under what circumstances? Where did they meet, Narn or EA territory?
On the Voice Acting. I think you should consider using no VA at all, if the alternative is the generated voice. Look at Fortune Hunters, it turned out great without a single piece of VA. If you do go for VA, I would first finish the campaign and make sure you proofread the dialogues and only then look for voice actors on the specific forum.