Yes, that is allowed. Public transportation tickets purchased centrally are considered a reimbursement in kind for travel expenses. For tax purposes—when it comes to business travel expenses—this falls under the specific exemption, just like a cash reimbursement.
The advantage: no individual expense reports; everyone gets the same ticket, and costs are known in advance. The disadvantage: you need to know where everyone is traveling from, and last-minute cancellations result in unused tickets.
Combine this with a clear registration process that includes a deadline.