Ec2MultiRegionSnitch or gossipingpropertyfilesnitch for aws regions

we have 3 nodes in us aws region and 3 nodes in singapore aws region. If I have to built a multi data center is it mandatory for Ec2multiregionsnitch to use or we can go with general gossipingpropertyfilesnitch. And can I use only private ip addresses for the both broadcast addresses and listen address here. As my system administrator told me we don't need public ip for these and private ip should work as both can communicate with each other. but i am little doubtful on this. Kindly can someone throw light on this. Thanks