I've participated in several Kelby Worldwide Photo Walks, and even led one myself last year. I haven't decided if I'm going to partake in one this year or not. I'm a little surprised the walk leader hasn't replied yet, but in my experience these walks are very social, casual affairs. I've shot everything from disposable 35mm to DSLRs while participating, and I'm pretty sure I brought a tripod on more than one occasion. Personally, I wouldn't sweat it. It's highly unlikely anyone is going to object to your use of a tripod, especially if the conditions favor using one.