Is buying lunch tickets for needy workers at the Center's restaurant considered charity, like feeding the poor, and is it possible to buy sixty tickets to feed sixty needy workers a full lunch?

Feeding workers is a charity for which you will be rewarded, as long as you intend it for the sake of Allah and the Last Day. This is a form of feeding that is not obligatory. As for obligatory feeding, such as for expiation, it is more prudent to give ownership of the required amount to the needy person. However, feeding a needy person two meals at the restaurant you mentioned is considered sufficient by many scholars.