It is definitely not legal to release PII of personnel in overseas, sensitive, or routinely deployable units, even for a FOIA request. 5 USC 552 b 3 and 10 USC 130 b. It's a specific FOIA exemption. We get hammered for emailing a recall roster to our own personal email, and some legal team thought, "Give out names to the press when the law says not to? This seems right."
Agree that there is no further public good that arises from knowing who the MP was.