So I recently heard of a theory which states that Ulfric Stormcloak actually calling Alduin with his mumbling when Tulius is speaking to him at the beginning. Now, do I believe this? No, there isn't enough evidence to even support such asinine claims, but what are your thoughts?

Agreed, you need some evidence to call it a theory, otherwise, it is just speculation. That doesn't make it impossible to be true, but I'm not aware of the story giving any reason why he would, other than the imperial suggestions that he is only concerned with his own gain and lust for power. The game does not answer these questions as far as I know. Also, if he could do this while gagged, could he not also use the Thu'um to free himself. Still, people are free to speculate.

Lol calling out Alduin to save his butt would be like being in a group fight and dropping a bomb under your legs. He could have just use some other shout to create trouble and run, not call back a deity that desires to destroy the world.

wouldn't he have to defeat/capture alduin? he's not just going to be ulfics slave because he can shout AL-DU-IN

Now that's just a terrible theory...