I think cron jobs will work on the SME server like on any other Linux distros. (At least I have had cronjobs running for some years withouth a problem.)
As an excample, edit your command on a text file and copy it into the directory /etc/cron.hourly/ and the command will be done one time per hour.
By the way, I can not remember for sure if I have done this with the rsync command, but I think it will work.
CORRECTION:
I thought it was a question og doing something again and again, but it was just to start one service ..
This can be done via editing the file /etc/rc.d/rc.local and the job will be done only one time at startup.
Don't know if there will need for some firewall "adjustments" from the shell .. (Depending of how it will be used.)