I see there is a bug, the @ signal is not accepted. I will fix it and will be available on Wildfly 14.
Thanks for reporting it.
There is a workaround, you can use the management model browser to add the xa properties, just create the xa datasource, do not test at the end.
Then click at "view" button, then at the right upper corner there is the "switch to expert mode", then go to "xa-datasource-properties" (left pane), then at the right add the properties. It is a bit more work, but you can do it in web console.
I am wondering anyway why this is working in your environment
At first, I didn't use the @ character as in your oracle url, but later I find it is not accepted.