The siphon will work if I understand your plan
The line to the sump will be enough
But, you need to be able to stop it when the return pump is off, so I'd suggest you don't do it unless you look into setting it up the same as a hang-on back overflow box with an in DT box, u-tube from box to fuge, and something like a Tom's aqualifter to restart the siphon after a pump restart
I'd also use a valve on the drain line to the sump so you can dial in the flow rate through the fuge
Have a look into how hang on overflow boxes work before you buy any parts
