Hi Courtney, The best source of info I have found re Hong Kong officials is on the Hong Kong Univ. digital documents website. Try www.sunzil.lib.hku.hk/hkgro/index.spto get in. I have found refs to John Lemm- lots of them, some naming him as an architect. It may not be 'your' John of course. I have been trying to set up an e-mail contact with the current day officials of the cemetery- by writing to them ! I will let you know if I have luck.
For others reading this; I know that John Minhinnett died in Hong Kong 5th Oct 1907. ( He was a minor civil servant.)I believe he was prob buried at Happy Valley. Is anyone based in Hong Kong willing to find and photo the grave for me ???