Probably. I haven't done it & I don't recomend doing it, because Bettas are better suited to smaller area's. If I were you I'd just get a small fish bowl to put the Betta in & put some other sharks & stuff into your redtails tank, liven thigns u a heaps
But if you must have them in the same tank, then get some plants, plant them around a corner or something, & that way the Betta will feel like it has a small enclosed area. If you do do this, make sure the Bettas spot goes all the way to the top, as it is a labrynth breather.