The forward lean or rake has nothing to do with aerodynamics, it's simply a slightly taller spring in the rear so that it will not sag too much when the rear is full of passengers and cargo. You can look at any vehicle and they all have a rake especially pick up trucks because of the heavy weight that can be put into the bed.
My gas mileage hasn't changed since the leveling lift and when the jeep is leveled it will have a more accurate oil fill reading rather than a jeep that has a rake. It would be no different then checking your oil on level ground as opposed to a slight hill.
I say do it as well, the Wrangler looks like a proper 4X4 when it's leveled out.