The quick answer to that is "Yes".
But the realistic answer to that is "Yes, as long as you have everything you need to get married".
You will obviously need someone to marry, but you will also need the local marriage license. This will allow the officiant (a minister, justice of peace, judge, mayor, captain of a ship) to marry you in Clark County. The place to get your marriage license and certificate is at the Marriage License Bureau on Clark and 3rd street in downtown Las Vegas. You can also book one in advance online thru (http://www.clarkcountynv.gov/Depts/clerk/Services/Pages/MarriageLicenses.aspx).
So, if you think your appearance is acceptable - yes you can get married in costumes and shorts and... most importantly you are not under the influence of drugs and alcohol (it's actually illegal in Las Vegas), then you can go ahead and get married.