Granted, he did "earn" it, but I always felt it was rather odd to supposedly be anti-government but yet still benefit from government money
Rather than anti-government I'd say JW's view themselves as anti war/killing.
I don't have a problem with someone getting the military pension they earned but It does seem ironic that some young JW's went to prison when they were young and their prison record made the rest of their employment life difficult, and the likelihood of having a pension of their own, possible. Years later, one of the elders in their congregation who did go to war and may have possibly killed someone, is now able retire (and possibly pioneer) on the pension he got for doings so.
It seems to me if the elder in question had a sensitive conscience, he might reason that according to his new beliefs, what he did in the past was displeasing to God (according to JW's) and to benefit from pension that was earned in that activity, might be considered a compromise of ones faith by some.
I think the Society leaves it up to ones conscience and I'm sure they'd gladly take the pension money for themselves if the elder in question couldn't bring himself to spend it.