If you have an oil-stained wolf or any other "glitch tamed" pet with a visual effect, you probably don't want to risk summoning it in a Timewalker dungeon.
http://us.battle.net/wow/en/forum/topic ... ?page=4#72
As we all know, if you bring one of these pets into arena they lose their special appearance forever. A similar system may be in place for timewalking. Here is the relevant bit:
Be careful!Most buffs are cleared when entering Timewalking, similar to Arena. This is necessary to ensure that the down-scaling that occurs when you enter the dungeon is done cleanly.
It's obvious at this point, from people who have lost their treasured pets, that this is confirmed.
Do not take these pets into Timewalking dungeons.