Yes, you can dry hop in your keg. The closer to serving that you add hops the more aroma you're going to get from them. The compounds responsible for aroma break down during the boil and they are among the first things to go when a beer ages. So if you're concerned about aromas from your adjuncts, I think you're going about it the wrong way.
It's hard to say without knowing the recipe, but based on your description I would still do the aroma hops in the boil and instead cut the dry hop.