In the case of suspected active acute or chronic pancreatitis, do the doctors normally perform ercp?

Sometimes: ERCP can be therapeutic in the management of some biliary pancreatitis, pancreatitis due to small stones, some types of sphincter of Oddi dysfunction, some cancers, and ascariasis infection. It is less important in diagnosis than it used to be due to the availablility of less invasive methods.

Absolutely: ERCP is a test that gives a picture of the "pancreatic duct", which is a tube that drains fluid from the pancreas into the intestines. Blockage of this duct often causes pancreatitis and the ERCP test is designed to show what is wrong. In some cases the ERCP can also relieve a blockage, leading to improvement in the pancreatitis.