yes, opiates tend to suppress the HPTA...especially one as heavy and longlasting as methadone.
Its really nasty shit (methadone). THe WD is worsethan heroin since the halflife is a LOT longer. He'd be much better off going onto subuxone which is a partial opioid agonist...it also suppresses your nuts much less and is generally more tolerated...
btw, I think the doctor that prescribed the test is a fucking moron. His levels would rebound after he gets done with methadone therapy...but now that he has started TRT he will probably have to do it for life...
best of luck