According technote Supported web browsers for WebSphere DataPower SOA Appliances
The list of supported browsers is specific to the DataPower firmware version and is documented in the Release Notes for each version. Use of an unsupported browser may result in missing configuration tabs or other unpredictable WebGUI behaviors.
So you may use other browsers, but at your own risk.
For convenience I copied the browser support statements for all currently supported firmware releases:
|XI release notes per release||supported browser statement|
|3.8.2||Microsoft Internet Explorer, Version 6 and 7 and 8, and Firefox, Version 3.5|