Hello,
Yes It's possible to manage tickets in more categories. The only condition is that the category flypage have to be set to: VMeTicketFlyPage.tpl
Yes It's possible to sell tickets of other sellers. You have to create them in the administration and then they can sell them on the cash desk (the front-end GUI). They can sell only the tickets, for which they have permission (good for licences with more parallel events). Only the cash desk sell is possible, there is no module for e-shops interconnection.
Here you can see some component screen shots:
www.artio.net/joomla-extensions/electronic-tickets
Tell me, what part of the system are you interested in, to make another screen shots.