The potential problem with keets is that they can become quite aggressive about pecking/biting. They become like mini bulldogs once they start doing that. This is usually the reason for keeping keets separate from any other kind.
Some people mix them with no problems, others have mixed results- some batches nothing happened but in another batch the keets might do something like tear up the eyelids, tear the top beak completely off a chick, peachick or poult..
It's similar to how some people report having no problems with adult guineas mixing with chickens or other poultry.. while others got rid of all guineas because they would not stop making life miserable for other birds. Kind of seems to go half and half in this case.