I got married in Las Vegas 5 years ago (didn't last...), and just had to give my state-issued ID and social security card. Because I married an mtf woman, we didn't have any problems with the gender markers... I was still legally female, she was still legally male. However, I imagine that if social security and your state license have the same gender marker, and it's the opposite of your partner's, you'd have no problem. Vegas doesn't require a blood test, and it's a pretty easy process to get the marriage license--- I was in and out in about 30 minutes.