Can someone get into my iPad, access my camera and turn on the webcam and record without my knowledge? I got an email that said they did.
Any app you install can (if you allow it) access the camera. So if you by accident installed such an app and granted access to camera and microphone, yes it‘s possible.
An attack through the Internet into an iPad with the most recent iOS version might be possible as well, but it‘s rather unlikely.
PS: The mail you got might just be spam though
This email is a scam. See this Gizmodo article about it.
Yes - there are people that can hack iOS devices, but no - they don’t email you. They sell their services for millions or more US dollars to defense contractors or governments because as soon as Apple figures out what isn’t secure, those holes get patched.