I've attended many of them over the past few years and brought a fighter to a couple. The knife fights are a lot less likely to produce injuries than those in which sticks, staff, or a two-handed rattan sword are used. It is way too rough for an old, fat, slow, marginally coordinated guy like me (although I do feel that I benefit from Guro Crafty Dog's regular classes).
The fighter I brought to two Gatherings was in his early 20s and had about 7 yrs of training under Vunak and others (he was a full instructor under Vunak and had his own school). He did well in his fights, including a couple against Top Dog, but still had several nasty bruises, etc.
Guro Crafty told me that when the original Ultimate Fighting Championships were getting ready to go on pay-per-view, they approached the Dog Bros. about the idea of an exhibition stick fight as a warmup event. However, after seeing tapes of Gatherings, they said something to the effect of "You guys are crazy---that's way too violent for us!"