Running ipmitool as a non-root user

/dev/ipmi* is usually restricted to root only as you've found. Your options for running ipmitool as a non-root user are (in rough order of my personal preference):

1. Use sudo (you can create an entry in sudoers specifically for people who should be allowed to run just ipmitool if you don't want to also give them generally unrestricted sudo access)

2. Modify your udev rules so the device is accessible by another user/group (I do not know where the udev rules are kept on CentOS 6, but look around under /etc for something that fits the bill). This is the same approach as editing devfs.rules - The CentOS documentation will lead you in the right direction and this page (or some creative googling) will help you out with the udev syntax. (I'd give you pointers but I'm barely conversant in it myself :x)

3. Connect to the IPMI interface over the network (if your IPMI interface supports this).
   This may require burning a network interface and crossover cable, or connecting the IPMI card to your network, which is why it's so low on the list.

4. Make ipmitool setuid-root.
   (Yeah. Don't do that. It's generally a bad idea and terrible advice - pretend I didn't mention it.)