Are camber plates needed with short stroke coilovers?

The camber will go more negative when you lower the car so you might want camber plates to adjust the handling.
I'm not sure what happens to the camber when you lower it and roll centre adjusters are being used

Camber shouldn't change much simply from lowering the car. Camber plates allow you to dial in more static camber and also easily get symmetrical alignment. If you're doing any sort of motorsports activities, you will need camber plates to get the most grip and any sort of decent tire wear.