Here's the deal. Most hospital's outsource the staffing of their full time emergency room physicians. You can't really ask if a individual doctor is in or out of network because they are either all in or out of network depending upon your insurance.
The folks that say, call the insurance and appeal are correct. Sometimes, practices will charge an "out of normal business hours" surcharge. Most physician practices will waive this charge if your insurance does not pay, but you HAVE to ask or they won't waive it sometimes.