The one possible quirk I'll try resolving around is right now the game server runs as a Linux branded zone on SmartOS, however normal syscalls to get arch will return 64 bit and it is indeed fully 64 bit (This is the first thing I've hit that isn't seeing it as 64-bit...which is why I think it's steamcmd's fault)
Instr's from https://developer.valvesoftware.com/wiki/SteamCMD