Well, I was actually thinking of more a morale/training thing. When you're in a group with other Valadeen, who have recieved the same training as you, you tend to work well together. For example, in the commonly encountered Fireball scenario, standard Valadeen procedure is for Soldier A to dodge low and to the right, Soldier B moves to the left and dives for cover, while Soldier C raises his shield to help divert the blast.
While the usual group of untrained, disparate adventurers would indeed get in each others' way, a group of trained soldiers and warriors, used to acting on instinct with their adjacent allies doing the same, would become, essentially, the quintessential well-oiled machine.
There's also the morale thing, for the rest of the bonuses. If Bob the Barbarian stands next to our favorite Valadeen soldier, he could care less, it's just some random stranger. But if another Valadeen stands by his side, his spirit is uplifted, and his morale boosted. One Valadeen is an army unto himself. Put two of 'em side by side, and nothing can beat 'em. This tends to make a heartened warrior fight all the better.
As for balance... maybe say that the bonus vs Fear and Compulsion is also conditional to another Valadeen being nearby. Or it's +2, +4 with another adjacent Valadeen. In all, though, it's not all that powerful. For one, a normal adventuring group would have to have at least two Valadeen warrior-types to truly take advantage of this, which leaves at least one standard archetype unaccounted for. Then they have to actually stay side-by-side. i don't know about you guys, but the players in my games are never adjacent to each other for more than a round or two, max, at the beginning of battle. The vagaries of war tend to seperate staunch allies quickly.
This would only be a real benefit when there are a lot of Valadeen together, where it would be nearly impossible to encounter one without another by his side. Say... in a large battle, where the Valadeen are NPC's. It would also make them a good low-level threat for high-level PC's, if it comes into play. A good, strategic mix of 2-3 level NPC Valadeen warrior-types who make sure to stay near each other and use solid tactics would make a great challenge.
Honestly, just compare it to the big two, elves and dwarves. It's still less powerful overall, even if you've got a party of nothing but Valadeen. And I personally think it fits perfectly with the flavor. Imagine yourself in a war. Would you feel better (and thus fight better) with a random soldier, or with your best friend since the 2nd grade fighting by your side? This could also be used as an RP tool. These people would by their nature have very tight, close bonds among themselves. To a Valadeen, any othe Valadeen is a friend since the 2nd grade, even if you've just met them five seconds ago. A natural camraderie.
I dunno, I like it. Mind if I borrow 'em, Mr. Prophet?