Steam pre-order bonuses do NOT apply to GMG pre-orders, regardless of the fact that all they're doing is handing you a Steam key, unless they specifically say so. One example I remember is that they did have some of those Professor Genki DLC keys for Saints Row The Third.
Right here, they're actually just poking the bear, saying "We don't believe in unlocking pre-order bonuses" and giving a couple of guaranteed free games. Though something about that deal is expiring after the weekend... I can't tell exactly what, since their advertisement is not very clear.