I have not. I think most users integrate into QRadar, which has a direct integration, but nothing to Splunk that I've seen yet.
There is a git repository that uses the Splunk REST API to send messages from the IBM Integration Bus found here. Currently it looks like the IBM developer network is having issues right now, so I can't really search it.
I see, surprised nobody has tried it yet. Unless they have and just haven't posted anything about it. Would be interesting to do though. Oh that's good to know, thank you for the info!