There is no limitations to what this system call can see.
Scripting call
System.isHostReachable(hostOrIp, timeout);is equivalent to this standard Java call
InetAddress.getByName(hostOrIp).isReachable(timeout);
My suggestion is to try to increase timeout parameter from its default value 1000 milliseconds to a larger value, for example 3000 milliseconds.
-Ilian