Again, for me it would be dependant on the guys attitude and how he was on stage (i.e if he was jumping about I'd be more inclined to say no).
I can understand why some people are unable to bring their own rig/a backup bass to gigs. I don't drive so bringing a second bass with me via public transport isn't always ideal (or at times possible). A lot of people seem to reply to this with "learn to drive then" but it's not cheap and unfortunately because of my age, insurance would be a fortune. My mate was quoted 6K insurance for a 3K car.