Converter 5.5 does not support RHEL 7. I suppose the following chain of events has ensued:
The parser has chosen RedHat (not enterprise) as default OS. Then it has decided to use BusLogic as SCSI controller. BusLogic OTOH is not supported anymore by RHEL 7. That at the end has caused the helper not to see the disk.
You may try to lure Converter believing it is RHEL 6 by editing the etc/*-release file on the source and try again. Keep in mind reconfiguration will fail(!) and XFS will not be preserved (I think the volumes will be converted to ext3 but do not guarantee).
Or wait for the next Converter.
Regards,
Plamen