i'm wondering if a few pygmy cories would fit in there?
otherwise yeh the otos would do well.
Make sure you take a bit of sandpaper over the metal before applying the silicon then it will stick alot better. Other than that I think it will be fine.
Or if you have the access to some tools, you might want to cut a circle of acylic to seal in at the bottom rather than using all that silicon.
....or use G4 pond sealant on the bottom.