The /pokemon command doesn't accurately show allowed tiers for mega evolutions. For example, when using "/pokemon escavalier" the allowed tiers are Ubers, OU, UU, and LU (http://i.imgur.com/uEyCnin.jpg). However when you use /pokemon on a mega evolution, it lists Ubers, OU, UU, LU, NU, and LC no matter what mega is tried (http://i.imgur.com/JAh3xUY.png).
Man I straight up said this in the post I made about it... http://pokemon-online.eu/threads/command-for-pokémon-tier-listing.31151/#post-441188
All fixed for next update. Megas and Aesthetic forms will both work properly now on /tier and /pokemon