Yes, there is a warning somewhere that states "NEVER back up a velke"
I knew it had something to do with the operator's safety, like one's feet.
A biggie is to have both feet on the velke when it jacks, and the trailing arm catches an ankle...
But you can also trip and have the mower on top of you quick.
So I think it's safe to say be careful.
There does exist a 2-wheel style that has the swiveling casters and the sulky itself never swivels,
and while it's probably the best type to use for this I still might be careful about calling it safe.
Ultimately we're not supposed to back up with it...
But, we do anyway.