It depends on who, what and where, and most importantly how the "offender" conducts themselves, I have a friend that's LE at the south rim, and does river patrols. He relates that since pot has become semi legal in many states, that folks don't understand that it's still illegal at Federal sites. They will issue a ticket for most anyone caught with it in the park, however how serious the ticket is depends on the offender's demeanor and how honest they are with the Ranger.
I can tell you that in my capacity as a river ranger, I put a lot of stock in how folks conduct themselves. I pull up to a camp full of drunken people and they decide to accost me with obvious lies and denials when I can see just what they were doing, well that gets them a ticket. If I pull up and am met with "I'm sorry, we didn't know, forgot, thought the ban was lifted", well they receive a stern reprimand instead of a ticket. Rangers, at least the ones I know, aren't out to ruin your time, but there are rules...
As far as mules, that's likely not going to happen, they are on a schedule hauling tourists and food etc, you get nailed poaching in GC, you're going to jail, your gear choppered out and possibly confiscated, and you left with the bill.. Chopper time is $ 5000.00 an hour.. Then you travel to either UT or CO to be arraigned at Federal court, bail set etc..
I totally get that we're all frustrated with the odds of getting a permit.. Poaching a river, especially one managed by a federal agency, well for me anyway, the possible pain if you get caught, vs. the opportunity to boat, well I don't know that I would take that chance, but that's just me. You get caught on Westwater, you'll likely be met by the Grand County sheriff at the Cisco ramp, same possibilities as Grand Canyon without the chopper bill.
Take the high road Bongo, never anything wrong with that, and lots of karma points should you need them.. The River god likes good karma.