For the record this is the error:
app|D Saving em1.1 NIC for host homer-sammy-hissem-clowser
app|W Not queueing Nic::Managed: ["Identifier has already been taken"]
app|W Not queueing Nic::Managed: ["Identifier has already been taken"]
app|W Not queueing Nic::Managed: ["Identifier has already been taken"]
app|W Saving em1.1 NIC for host homer-sammy-hissem-clowser failed, skipping because:
app|W Identifier has already been taken
app|D Saving em1.2 NIC for host homer-sammy-hissem-clowser
aud|I create event for Nic::Managed with id 360
app|D Saving em2.1 NIC for host homer-sammy-hissem-clowser
aud|I create event for Nic::Managed with id 361
app|D Saving em2.2 NIC for host homer-sammy-hissem-clowser
aud|I create event for Nic::Managed with id 362
app|D Saving em3.1 NIC for host homer-sammy-hissem-clowser
aud|I create event for Nic::Managed with id 363
app|D Saving em3.2 NIC for host homer-sammy-hissem-clowser
aud|I create event for Nic::Managed with id 364
app|D Saving em4.1 NIC for host homer-sammy-hissem-clowser
aud|I create event for Nic::Managed with id 365
app|D Saving em4.2 NIC for host homer-sammy-hissem-clowser
aud|I create event for Nic::Managed with id 366
app|D Saving ipmi NIC for host homer-sammy-hissem-clowser
aud|I create event for Nic::BMC with id 367
app|W Unable to assign subnet - reboot trigger may not be possible, primary interface is missing IP address
aud|I update event for Host::Base with id 260
This is from discovery but the same result would be from Foreman core parser.
Workaround: use biosdevname=0 on the kernel command line to go back to pre-RHEL6 naming convention.