If you want to use UINotify plugin with XPerience and have the icon work as well you'll also need ImageLibrary plugin on your server. After that setup the UINotify plugin as you want with XPerience own message section so only it uses that specific message. Go to the admin panel in XPerience and setup the UINotify options the way you want for the messages and enable. In the UINotify config you can enable the image and copy this address for the image: http://www.skilledsoldiers.net/Rust/XPerience80.png
In UINotify for that message use these settings:
"Title Key (lang)": "XPerience",
"Image Settings": {
"Enabled": true,
"Image": "http://www.skilledsoldiers.net/Rust/XPerience80.png",