The only problem I see is that the water level is likely far below the rim whereas a tank has water close to the top. That could affect the output of the pump since it has to pump higher above the water level.
I've got my Remora Pro in my sump right now. I bought it before I added a sump to my system and didn't want to spend money on another skimmer (in-sump). When I first added it into the sump, it hardly pulled anything out for a whole month. Even lowering the collection cup all the way down did nothing. I had to raise the water level in the the sump as high as possible before it would finally start pulling anything out. As soon as I did that, it started skimming as well as it did when it was hanging on the back of the display tank.