Here is a quick HMC one line script to run a command on every VIO server attached to the HMC. It uses "viosvrcmd" which uses RMC so there is no SSH keys or anything to setup; it just works as long as RMC is working in your environment.
In this example, it runs the "errlog" (aka errpt) command on every VIO server. You can change this to whatever command you would like to run. The script looks through all managed systems for VIO partitions, and attempts to use viosvrcmd to run the specified command on each VIO server.
for sys in `lssyscfg -r sys -F name`; do for vio in `lssyscfg -r lpar -m $sys -F name,lpar_env | grep vioserver | cut -f 1 -d, | sort`; do echo $vio; viosvrcmd -m $sys -p $vio -c errlog; done; done