If you are stuck on the strip and want to eat someplace that is vegetarian friendly, head straight to the Wynn and Encore Resorts. Each and every restaurant at the casinos there has a complete and separate vegan menu!
We have eaten at several places there, but I singled out Botero, because it has the more unusual veggie fare of the bunch. We bought a bunch of smaller items and did a lot of sharing and everything was wonderful.
And for the locals, don't forget about the Wynn Resorts for your special ocassions... It's such a relief to find a veggie friendly place where you can show up in dressy attire and have candlelight and romance.