I don’t think contamination should be a huge concern, but I took a similar precaution. My last wit came out as one of those beers where I simply wouldn’t change a thing. Going into the fermenter, it smelled simply amazing. zest of 4 different citrus, coriander, freshly crushed by me, and dried chamomile.
Once fermentation had finished, I wanted a little more, as I felt like a lot of the aromatics had been blown away during the ferment. I added 2oz of dried chamomile (fresh maybe would have been better) and zest of another orange to a sealed container and covered with vodka for about an hour. I discarded the vodka (tried and smelled it, it didn’t seem to absorb any of the aromatics) and added the material to the fermenter (you could do the same w/ a keg, though I would highly recommend a string and muslin bag). Again, it is one of my favorite beers I have made. Something about me doesn’t trust the tea route, as I’m not sure if all the aroma compounds become soluble that quickly. Then again, I’m not sure they become soluble in the beer either.
I don’t know how people keg wits (though many do). Tasting the beer with and without yeast in the pour, I note significant differences in flavor and aroma. IMHO wits need yeast when served and other than agitating the keg with each pour, I’m not sure how you get that.