Magnolias are beautiful, and I think they would be a lovely addition to your tent!  I don't think it would look too “holiday” at all.  The leaves are so green and beautiful – I'm sure it'll add nice color to your decor!

I am helping my sister-in-law decorate a tent as well, and we were thinking of making flower garlands that hang down in strands.  I think fresh garlands are an elegant touch!  Good luck with your tent decorations.