Yeah I was about to post this.
The Howard Hughes film Beatty wants to make is a comedy and is set in Hughes later years. I think the film "The Hoax" came out just after The Aviator and was a Howard Hughes film (sorta).
I think Nolan will be able to make the film as the two of them will be totally different films. The Aviator and Mr.Hughes were both serious in tone, both big budget and would have come out roughly the same time.
It was a similar thing with the film Alexander where both Baz Luhrmann and Oliver Stone were making the biopic for different studios. I don't think it will be the same thing again as Mr.Hughes will be aimed towards the Oscar season (2013 guess as the script is pretty much ready) with the Beatty version coming out another time most likly much earlier and looking for a diffrent film crowd.