It's services that you connect a contract to, not the queue. When you have a conversation between 2 services in the same database, it is even very likely that 2 queues use the same contract.

So yes, you can re-use the same contract for multiple services.

Also, you can create multiple services connected to one and the same queue. Since each service can have one or more contracts and there doesn't need to be a connection between the contracts on these services, you can also have messages from multiple contracts going into one and the same queue.