Yes, you can have multiple queues on the RabbitMQ instance and a server can also publish messages.

There isn't any performance issues with the scenario you described. The publisher will need to use two or more clients (one for each service) and instead of calling

  await clientA.GetAsync()

it will call

  var resA = clientA.GetAsync();
  var resB = clientB.GetAsync(); 
  ...
  var resAll = Task.WaitAll/Task.WaitAny(new Task[]{resA, resB});

to wait for all clients to complete.