Actually I recall reading that ESSM has been tested in the terminal BMD role, specifically as a counter for the DF21D.
It looks like SM-6 will be tasked to perform the terminal phase BMD role supplanting SM-2. It would be great if ESSM could also help out but it seems the USN needs to acquire a surrogate target vehicle to emulate the ASBM to test out if's terminal phase defense.
From the June 2014 Congressional Research Service report on the Aegis BMD Program:
Target for Simulating Endo-Atmospheric Flight of DF-21 ASBM
Another potential oversight issue for Congress concerns the lack of a target for simulating the endo-atmospheric (i.e., final) phase of flight of China’s DF-21 anti-ship ballistic missile. DOD’s Director, Operational Test and Evaluation (DOT&E), in a December 2011 report (DOT&E’s annual report for FY2011), stated: Anti-Ship
Ballistic Missile Target
A threat representative Anti-Ship Ballistic Missile (ASBM) target for operational open-air testing has become an immediate test resource need. China is fielding the DF-21D ASBM, which threatens U.S. and allied surface warships in the Western Pacific. While the Missile Defense Agency has exo-atmospheric targets in development, no program currently exists for an endo-atmospheric target. The endo-atmospheric ASBM target is the Navy’s responsibility, but it is not currently budgeted. The Missile Defense Agency estimates the non-recurring expense to develop the exo-atmospheric target was $30 million with each target costing an additional $30 million; the endo-atmospheric target will be more expensive
to produce according to missile defense analysts. Numerous Navy acquisition programs will require an ASBM surrogate in the coming years, although a limited number of targets (3-5) may be sufficient to validate analytical models.
A February 28, 2012, press report stated:
“Numerous programs will require” a test missile to stand in for the Chinese DF-21D,
“including self-defense systems used on our carriers and larger amphibious ships to counter anti-ship ballistic missiles,” [Michael Gilmore, the Pentagon’s director of operational test and evaluation] said in an e-mailed statement....
“No Navy target program exists that adequately represents an anti-ship ballistic missile’s trajectory,” Gilmore said in the e-mail. The Navy “has not budgeted for any study, development, acquisition or production” of a DF-21D target, he said.
Lieutenant Alana Garas, a Navy spokeswoman, said in an e-mail that the service
“acknowledges this is a valid concern and is assessing options to address it. We are unable to provide additional details...
