I believe this was caused by missing compute attributes that would specify at least one interface which caused fog to create a vm without any nic so Foreman couldn't load a mac. To create the host properly on libvirt compute resource, you have to specify --interface argument as well so it will create at least one interface, e.g.

# hammer -u … -p … host create \
        --architecture-id 37 \
        --domain-id 42 \
        --environment-id 81 \
        --location-id 258 \
        --mac 'a9:1a:9a:70:be:60' \
        --medium-id 32 \
        --name 'AkqttNPO2' \
        --operatingsystem-id 43 \
        --organization-id 259 \
        --partition-table-id 28 \
        --puppet-proxy-id 1 \
        --root-pass 'changeme' \
        --compute-resource-id 22 \
        --interface type=network           # <--- this is important

After we match interfaces with compute interface (introduced in 1.8) this is no longer an issue. If you see this behaviour on Foreman 1.8+, please reopen the issue.