If I play Void Rush and reveal 2 Trifarian Glory Seeker, do I get the Legion effect of the Trifarian Glory Seeker to give it a buff?

No, you do not get the Legion effect for the Trifarian Gloryseeker played via Void Rush.

According to Rule 738.1.c.1, the Legion condition for "on play" effects of permanents is: "If you have played another Main Deck card before this one already this turn, apply [Text]."

When you play Void Rush, it is the first card you are playing this turn. Because Void Rush is the card that allows you to play the Trifarian Gloryseeker, the Gloryseeker is the second card played in the sequence. However, the Legion condition checks if you have played another card before the card with the Legion ability.

Since Void Rush is a spell and not a "Main Deck card" (it is a card you are playing from your hand/deck, but the Legion condition specifically looks for a previously played Main Deck card), and because the Trifarian Gloryseeker is being played as part of the resolution of Void Rush, you have not met the requirement of having played another Main Deck card before the Gloryseeker was played.

Therefore, the Legion condition for the Trifarian Gloryseeker is not satisfied.