I've followed the documentation for 12.1 very carefully, especially with regard to OS library levels. However, libdb-4.3.so and/or libdb-4.7.so seem to be missing. There's not much on MOS about it, a couple of community discussions and someone saying they installed the db4 and db4-devel packages to get it working. However, those do not appear anywhere in the documentation.
What is Oracle's supported method of getting these libraries on there? Where is the comprehensive list of OS libraries required for 12.1 and 12.2 on 64-bit RHEL? Support note 761566.1 is apparently incomplete.
All the required packages are normally listed in the doc you have provided. You will be able to get it easly by using E-Business Suite Pre-Install RPM method mentioned in the note.
RDA - Health Check / Validation Engine Guide (Doc ID 250262.1) - check requirments using 12.1 installation rule set available
Are you getting any error during install process?