I agree with you... Probably not the day of the wedding. I would be ok with them going to day before and if they extend the invitation to other guest as well, making it part of the wedding weekend activities.
My FI and all the boys and some of the girls are doing golf the morning of the wedding and later renting ATVs and going out exploring... The scary part for me, is that my FI is really into extreme sport, so I'm just hoping that he doesn't do anything STUPID!!!