I have a client setting up a Hadoop cluster. We have all used and are very familiar with CentOS 7. I was told Scientific Linux maybe better optimized for Hadoop.
Is there any truth to that?
Maybe Why Scientific Linux was made and the Design philosophy will answer your question. As a scientific distribution it supports the installation of scientific software, which is sometimes available as source code only.
So, depending on the goals you try to achieve within your infrastructure, Scientific Linux might be a good choice. But it is not explicit optimized to serve the Hadoop framework/stack.