In my opinion, if you are battling someone that accepts Smogon's teiring system, and you are requesting an OU Standard battle, you should be prepaired to face them, wi-fi battle, or otherwise.
I know you can't use them legally on wi-fi without the use of an external device, but whoever it was was using Smogon's tiers, not Nintendo's.
Generally, if you place in your siggy you don't want to battle Rotom formes, and you are the one requesting the battle, if someone is using them, they won't battle you. If you don't have something to that nature in your siggy though, be prepared.