I always forget how to do this and end up Googling for the answer. You may be doing the same right now.
The following example is on vSphere 5 with a Centos 6.x guest OS but I assume it will work with RHEL as well.
1) Initiate the VMware Tools installer (Guest -> Install/Upgrade VMware Tools)
2) From the command line in the Centos guest OS:
i) Mount the CD/DVD ROM drive
# mkdir /mnt/media
# mount /dev/cdrom/ /mnt/media
(You should get a message similar to: mount: block device /dev/sr0 is write protected, mounting read-only)
ii) Copy the installation files from the media to a temporary directory
# cd /mnt/media
# cp /mnt/media/VMwareTools-8.6.0-446312.tar.gz /tmp
(Note: Your filename might be slightly different, so you could use cp /mnt/media/VM*)
iii) Extract files from tar
# cd /tmp
# tar -xzvf VMwareTools-8.6.0-446312.tar.gz
(-v is for verbose output. This lists each file name as its read from the archive)
iv) Run the VMWare Tools install script
Follow all the defaults by pressing “Enter” key.
When finished the media will eject itself automatically.
This should successfully install VMware tools into your Centos OS