This is the second time I've been through the tower so if the trainers change every time you go through it's probably in the second batch. The "batch," if there is one, contains two trainers with Picknicker sprites, Red, Brendan, James and the invisible trainer.
As you can see from the picture above there is no overworld sprite for the trainer yet I am in battle with them. I wasn't expecting it so I wasn't able to get a better picture but that's pretty much all there is ... or isn't.