When we go into a sushi restaurant, there is (1) one who takes reservations - when the restaurant is not quite a big one, this one will be (2) the manager or its proprietor. What do you call this persons, (1) and (2), respectively in English? (For (2), some places call them just 'manager,' and some places call them according to their ranks, gwa-jang (section chief), bu-jang (department head) in my country.)
There isn't any specific English nomenclature for employees at a sushi restaurant. I have not been to any sushi restaurants that refer to their employees by the Japanese name of their position, but I'm sure they exist in the country somewhere.
Colloquially, managers are simply called that -- managers. There is a difference, however, between "the manager" and the actual owner of a restaurant. Managers are in charge of the restaurant while the owner is not in the office.
To answer your main question, I think Jason S described it adequately -- the person that takes reservations and seats guests is called the host or hostess, depending on gender. Those who serve food to the guests once they are seated can be called waiter/waitress, server, or steward/stewardess.
Most likely that would be the host or hostess — at least, this is what you would call the person at a restaurant who greets you and brings you to a table. (as opposed to the waiter or waitress or gender-neutral server who takes care of you once you're seated)