File::Fetch is not in check_modules.pl. It needs to be added.
What version of File::Fetch is installed with "yum install perl-File-Fetch"? One way to find this is to run
perl -MFile::Fetch -e 'print $File::Fetch::VERSION;'
I don't think this is a WeBWorK bug. Something is not working with your File::Fetch installation.
You can use the OPL-update-legacy script, but that will take a while (around 10 minutes if your computer is fast).