Nope there are some spoilers in just about everything even Raider Wars. Earth Brakiri War would be one that shouldn't spoil anything in the show.
Except the existence of The Shadows
, but it's likely that anyone watching the show for the first time will have heard of them, even if only in passing. Also, by the time the friend 'currently watching the show' views episode 13, that's out of the bag, so...
Well... not really. Episode 13 only establishes that something is out there. Even the name is just something a seer mentioned.
You only really learn what the Shadows are when you get the first "Millions of years before, there were beings...." explenations from Delenn. Which would make it episode 38 "In the Shadow of Za'ha'dum".
I would tell him to watch, at the very least, the complete first season and the first two episodes of season two before playing Earth-Brakiri-War.