Word for a person who meets all the guests at the entrance

If they are meeting the guests to welcome them, I'd call them the host. Or, if they aren't actually the host but just an emissary for the host, I'd called them the greeter.

As mentioned in the comments, if they aren't there to welcome but to vet they'd be called a bouncer.

You should consider usher.

ODO:

usher NOUN

1 A person who shows people to their seats, especially in a theater or at a wedding.

‘Sarah and Paul have asked me to be one of the two ushers at their wedding.’

American Heritage Dictionary:

usher
n.

2. One who greets guests at a wedding and escorts them to their seats.