With SwiftMQ Explorer open the message viewer and press the chart button. It displays you the rate of the queue. Same can be done on JMS connection level with the frame of JMS Swiftlet / Usage.
Re: Monitor enqueue & dequeue rates for a message queue?
No problem. SwiftMQ Explorer is based on CLI and so is JMX. So you can query any attribute of SwiftMQ's management tree by JMX. Look here. There's a sample on that page to query a queue's message count and display it as graph. You can also query the management tree programmatically by use of the CLI Admin API. CLI itself is documented here.