Hop tea is typically used in the fermenter, not the keg. If you use some DME and add it to the keg with the hop tea you are adding unfermented sugar to the cold beer.
I've never tried what you are asking, but I asked an experienced brewer the exact same question last year. He said that it would put huge grassy flavor in the beer...don't know, but that's what he told me.
I don't usually follow other people when it comes to beer...I listen to all and make decisions based on everything I hear, even from less experienced brewers.
In your case, I suppose you are trying to get more hop aroma/flavor out of the beer in which case I would weight down a bag with 1/2 oz or maybe an oz of hops and slowly lower it into the keg with a piece of fishing string or sewing thread...all sanitized by boiling of course.
If I were to try doing what you are suggesting, it would be like this...boil a cup of water, kill the flame and add the hops, strain it after 10-20 minutes covered and add the liquid to the keg, or better yet, add a squirt to a glass of beer and test before chancing the entire keg.