they can not take cash.
no tip is needed.
If the host went above and beyond the free nights and food such as free show tickets, you could give the host some type of gift, maybe a nice bottle of wine. (don't forget to have the clerk at the store put a gift sticker in the box , buy the gift in Vegas).
I once took a box of chocolates for the host. The check out clerk in the vip check out took care of all the room charges himself. I never saw the host. I went home paying 0 and he went home with a box of chocolates