I think technically what they sell is services related to RHEL and not it itself (correct me if I'm wrong).
To me at least, a big problem with it is the hypocrisy. RHEL started itself by repackaging another piece of software. Why is it not OK for others to do the same to them? Especially when the gpl license allows that, and requires them to allow that!

The Linux license allows anyone to distribute it for profit (under certain conditions). If I wanted to sell CDs with the Linux kernel I could. Wouldn't be a good business, but I could.