So what you usually do is:
1- create a /etc/rc.d/rc.fetchmail script which knows how to start, stop and restart (take any of the standards scripts as examples); make that script executable (chmod +x)
2- in rc.local, add
if [ -x /etc/rc.d/rc.fetchmail ]; then
It's a normal script so you can do whatever you like, there's no restriction.