Relicanth has 55 base speed. This is not good enough to outrun Timid/Jolly scarved base 90's, let alone stuff like Scarf Palkia, even in rain. If Relicanth has just a little bit more speed (enough to outrun Timid scarf Kyogre) he would be awesome, but as it stands, Reli isn't that easy to use effectively. Bear in mind that Giratina-A and Ferrothorn are everywhere...
Relicanth, like Kabutops, hits very hard and can check EKiller. That alone makes it viable. With that said, I'm not sure a little extra base power in its main STAB move (Head Smash vs. Stone Edge) compared to choice band Kabutops makes it worth using over the latter. Kabutops can outspeed almost all standard scarfers barring Terrak (which it kills with CB aqua jet); Relicanth cannot. It's still cool that you are using it though.
Tornadus formes are not viable in Ubers. They are too frail and simply cannot hit hard enough. Choice Scarf 100% accurate hurricane in rain might seem nice, but compared to Kabutops' choice band waterfall, it falls short. Tornadus also has zero defensive staying power, and Uturn hits like a girl.
Edit: I have found 196 speed scarfers to be rare sights, except Dialga. Never assume aCS Kyogre will be slower than Relicanth because thunder obviously destroys it.