i'm assuming from your diagram that you're drilling a hole in your tank. if so then yes that would work but your water line would end up on the bottom end of your horizontal pipe not the top end
as long as the return flow is less than the overflow and as long as the sump tank have enough spare space to hold all overflowed water during power failure, its good. and at least 1 redundant system is a good idea in case you have overflow blockage
Thanks, that helps a lot. I'll be sure and keep that info in mind when I build the system. It's for my balcony aquaponics system so if anything fails I won't have to worry about water getting everywhere, but my wife will be sad if I kill the goldfish though...
edit: Its just a plastic tub so I figured drilling a hole will be a lot easier then building a hob overflow.