Theres no heavy symbolism, because the players are loaded enough with significance all by themselves...
I agree that the players and the occasion are quite significant. And there may not be heavy
abstract symbolism (as in "the green, orange & white in the stained glass window each represents..."). But this is the largest ensemble scene in the film (2nd only to the July 4 scene) with very significant players – some of whom we see for the only time. And this is Ang Lee!
So I do think the blocking and the angle would be set up carefully, with a consistency and carry-through regarding the rest of the story.
There is something noticeably unique about the blocking! Normally, the best man and maid of honor act in parallel – either turned in the same direction or mirroring each other. Here, the maid of honor faces inward toward the wedding party, while the best man faces forward.
I think this is a visual shorthand for the roles they play. Alma's sister will be a personal, practical help for the couple, looking after their offspring. K.E. – who faces the priest and the altar, and faced Earl with Ennis – provides a male role model and reinforces convention. He + Ennis are separated in the frame by the priest – possibly illustrating how they come down on opposite sides of a major moral rule?