Traegers are not an uncommon sight at contests, they are legal to use. I'd like to get one myself at home, but as long as my Weber bullet isn't rusted through I will keep using that one.
The biggest problem that Traegers have is they "don't travel well". They are great for your patio, but to load, transport, unload, cook, load, transport, and unload again at every contest... they are pretty fragile. Their legs aren't sturdy enough to take that kind of abuse very often. They are also pretty thin gauge steel, and that's a problem when the weather turns bad. Again, OK for your patio because you'll just decide to cook another day if there's a pouring rain, but at a contest you have to deal with the elements. The other thing is the Traeger will need electrical power, either from a generator or a hook-up of some sort. That's not as big a deal as you think. At a contest, if you use supplied power it will get turned off if there's a t-storm but someone nearby will probably have a generator they'll let you plug into.
What's also common are for heavy duty smokers to have a pellet auger and controller, same as a Traeger, but much more physically substantial.
I'm pretty satisfied with the ABS Judge our team uses (one of the guys owns it). Load it with 40-60 lb of charcoal, a log or three of fruit-wood of your preference, and let her go all night.
http://www.americanbarbecuesystems.com/abs/Judge.html
edit:
Oh, yeah, these guys:
https://www.gatewaydrumsmokers.com/
are getting more and more popular, too. They cook hot and fast, so no more 13 hr butts. I think people are saying they can cut that down to 5-6 hrs. For $800 they are the latest thing. I've seen teams with 4-5 of them lined up.