I am running Oracle Linux 7.3 and I am getting this issue as well:
Do you want to use OCS-Inventory SNMP scans feature?
Please enter 'y' or 'n'?> [y]
Do you want to send an inventory of this machine?
Please enter 'y' or 'n'?> [y]
Setting OCS Inventory NG server address...
Looking for OCS Invetory NG Unix Unified agent installation...
sorry, can't find ocsinventory-agent in $PATH
make: *** [install] Error 1
I found that when I downloaded the tarball it was not in the root ~ directory. I moved it to root's home and reran perl Makefile.PL and make install. This time around it installed correctly.