BIS_fnc_EGSpectator offers a function "IsLocationIdUsed", but the code does ignore input.
case "IsLocationIdUsed" :
{
private _locations = missionNamespace getVariable [VAR_LOCATIONS, []];
private _index = -1;
{
if (_x select 0 == _id) exitWith
{
_index = _forEachIndex;
};
} forEach _locations;_id is not defined, and should probably be
private _id = _params select 0;