Charedim generally do not eat Rabbanut Hashghcha.
How many Badatz places hire the Rabbanut mashgiach to be their mashgiach as well?
Many of them.
Chareidim may think they’re getting a Badatz hechsher, but in reality, are getting the regular Rabbunut.
(Source: a friend of mine, a Rabbanut mashgiach by trade, and hired by several Badatz hashgachot as well in the same places.)