Elf I’ve only been once for NYE so I’m no expert. You might want to post your question on Vegas Fanatics as there seem to be quite a few experienced NYE posters.
What I’ve been told is, they shut down entry into casinos to those without room keys at some point. I would think there will be provisions in place for concert goers to get back to there hotels. Maybe your host can advise?
Sounds so exciting seeing Bruno Mars. I’ll be at PH the 29-1, if you have a chance would love to meet you.