I've heard that they've used a Shure SM57 mic for the Winfield contests, so it obviously can work well enough. I've recently been studying the SM57 frequency response charts, however, and it surprised me to find that with close miking, the strongest proximity response of the mic is at 200 Hz. 200 Hz is a pretty boomy frequency for guitar, so the typical soundman's response (including my own) is to roll-off the bass end at the mixer. The downside of that is that you must roll off a great deal of the deep bass to get 200 Hz down to an optimum level.
Here are some frequency response charts for the SM57, including one that shows the proximity effect at 1" away and 2" away.
https://www.google.com/search?q=SM57...w=1003&bih=644
On the other hand, if you're miking from a greater distance away, the SM57's frequency response will still be much stronger at 200 Hz than 98 Hz (low G on a guitar in standard tuning at concert pitch) or 82.4 Hz (low E on a guitar in standard tuning at concert pitch).
It seems to me that the suggestion for using a Shure SM81 will serve you better. The mic can be set for a relatively flat bass response, and if you need to roll off some proximity effect because of close miking, rolling off the bass at the mixer will give you a more even bass roll-off than you'll get with the SM57. The one caveat is that your mixer must have phantom power to use the Shure SM81. Most mixers have it.
A parametric EQ could help you get a flatter response for the SM57, but I doubt that you'll want to get into that particular patch of weeds.