Make sure the hostname Observium uses matches the hostname that Smokeping uses:
+ sw1_hex host = sw1.hex
For the category name, Smokeping does not allow dots, use an underscore instead.
Similarly the hostname used by Slaves should match the hostname used in Observium.
Hosts shouldn't be arranged in any groups or hierarchy.
$config['smokeping']['dir'] to the correct directory:
$config['smokeping']['dir'] = "/var/lib/smokeping/";
You should now see a smokeping tab on each pinged device, and each Smokeping server.