i think it might be simpler to have your arcade rom folder on the server: https://github.com/RetroPie/RetroPie-Setup/wiki/Running-ROMs-from-a-Network-Share
this way, the mame .hi files themselves would be also on this server (see https://github.com/RetroPie/RetroPie-Setup/wiki/lr-mame2003#high-scores), so you would both be using the same individual files. i guess you wouldn't be able to log scores on the same game at the exact same time.