I do have an in tank backup float to ensure if my tank level gets too high my ATO disables, but having one for the pump is a good idea too. I have the floats available, and my pump is on a smart outlet I can control from my reef pi, so I might as well do that. Doing it also in the hob overflow compartment by daisy chaining two floats together should be pretty easy too.The biggest concern is the siphon tube getting blocked by a snail or something else and then your siphon breaks. I have made my lid of my tank so that nothing from the DT can get into the weir box unless it can fit through the weirs.
But if your tank can hold the excess amount of water from your return chamber and you sump can hold all the water than siphons down from flow being off then I don't really see any issue.
Getting the return pump water level consistent is the only hurdle in your specific setup and once that is solved then you should have a smooth/safe running HOB overflow setup.
I am going to add one more safety to mine in addition to my low water level cutoff switch for the return chamber. I will add a high level safety switch to shut off the pump if the water level in my external overflow box gets too high. For my specific setup that should cover all possible flooding situations. My 1in gate valve has to be closed down pretty far (wish I went with a 3/4in drain line) so clogging/reduced flow can happen over time pretty easily I presume which would cause the water level in the external side of the HOB to rise.