Vegas Steakhouse that's not particularly formal?
I'm not aware of any steakhouse that suggests jacket and tie. That standard is reserved for only a couple of top dining spots (none of them steakhouses). Most of the better steakhouses will specify something like slacks and a buttoned shirt or perhaps polo jersey; even that won't be strictly enforced.
My favorite steakhouse is CUT, if price is no object.
Last summer a friend and her daughter were in town and I visited them at their hotel. I didn't know they were wanting to go out to anything fancy for dinner and was just wearing shorts and a nice but not fancy t-shirt. They felt like going to a steakhouse but I was a little concerned due to what I was wearing. We called a few places and they all suggested at least a collared shirt and preferably pants. Finally we called the Golden Steer and they said "The only thing we suggest is that you wear a smile", so that settled it, we were going there. We did and everyone loved it. The food was excellent and the service was great.