Absolutely. It's just good sense to be nice to the sound guy (or gal). Wherever I've worked, whether at the day job or in bands, I've made sure to be friendly to security/door staff, sound people, bar/wait staff and similar. They can ensure you have a pleasant experience or make life awkward, so, even if you look at it from a purely selfish point of view, it's a smart move to be nice to them.