Hey Rob,
All my images are taken with a EQ6pro and a 12" newt, so for people to say its not possible is just simply lack of either trying and or knowledge.
Simple fact is the mount's gears are rated to 25Kg's and i push it beyond that. In fact my mount has tracked efficiently taking decent photos for two years now without a single service.
equinox guidescope, Parallax rings (weigh a tonne), 35mm Large format CCD camera, Titan guidecam and 12" Newtonian.
Proof is in the "DOING" not in the talking.
There is no reason i can think the NEQ6pro will not be able to carry a 12" Meade EASILY although i do agree focal length will start to play an important role, however Deep sky imaging would not be what you'd be intending to do with it anyways i would assume as it is not its' strong suit.
http://www.theastroguy.com.au/photoalbum.html
Iv'e taken images of galaxies nebulae and even faintest stellar objects with that rig.
Regards
Shane