SELinux is a MAC (
Mandatory Access Control).
The basic idea of a MAC is that it is a security guard for your operating system. It watches the applications (like squid) and stops them from doing stuff it thinks they're not supposed to do. This can break some applications in some circumstances unless everything is configured properly.
To answer your question: Yes, SEL can be used to help secure squid. But, that's not the only thing SEL is for and there is a lot more to
hardening squid than just controlling MAC in the underlying OS.
Since you provided literally no information of any kind what so ever the best I can do is give you generic platitudes:
RHEL/Squid/SEL
Protect Squid service via SElinux.
