Well if you think about this question you would not know if there are two different styles vs. one another. All would simply fight by the rules of the competition. You would simply see a WTF competition with all players doing the same thing, regardless of their styles. That same would be true for ITF competitions also. I have been to many OPEN tournaments and know people that were from different styles. I have seen Karate people at TKD tourneys, as well as Kung Fu people as well. Even saw some Westcoast Martial Arts competitors at a WTF style OPEN tourney. I have even seen and talked to some WTF competitors that fought in ITF and Karate tourneys.
Gorillas kids are WTF trained but now compete and train in Karate tourneys as well as WTF trouneys still.
Now if you are asking if there is a specific tournament that only has WTF people fight ITF people, I don't think that exsist. What would the rules be? And if you said just fight by your own rule sets for each org then how to you ref that? If I was doing WTF style and then punched to the face did I violate the rules. You cannot have a fair or safe competition with two people using two different rule sets. No ref would even be able to manage that.
So yes I have seen WTF and ITF people compete togeather but they are alway only doing one or the other.