Why the heck would a theatre NOT ALLOW the actors to do them? Even if the only effect is that of a Pep Rally. If it helps to prepare the actors, either physically or mentally, it would seem to be a good thing.

In my current role I need to perform a similar warm up that singers would use as I spend half the show impersonating a woman, and falsetto is tough on the vocal cords. Especially come the Sunday matinae (sp? help!!). Some of the other actors perform breathing excercises, vocal excercises, or just sit quietly while waiting for curtain, depending on individual preference. Before the show we do something called an "energy circle" which seems kind of weird to me; but if it relaxes the others, why not?

Haven't heard of the chants, though.

I definitely believe in warm ups, usually not a pep-rally sort, but things for individual players, like tongue twisters to get your speaking voice warmed up. The most useful exercises involve hard to speak sounds, or sounds that are hard to distinguish one from another, i.e.;

Around the rough and rugged rock the ragged rascal ran.

Red leather, yellow leather.(looks simple, doesn't it?)

A skunk sat on a stump, the stump thought the skunk stunk, the skunk thought the stump stunk. (that's even hard to type)

And my personal favorite:
You know New York, unique New York.
I guarantee that if you use this one, "Yew Nork" will become a usable word in your cast vocabulary!:)