I know both Alfalfa and Perennial Peanut hay are similiar nutrition wise, but I'm wondering if a horse can't tolerate alfalfa, would they be able to tolerate the perennial peanut hay?

The answer is probably "no", but didn't know if any one has any experiece with this.

Bump

What do you mean by can’t tolerate? Does it make them colicky? Hot?...

The only problem I have had between the two is that with the perinneal peanut hay the horses don't drink as much extra water.  So, for my horses that go on the road, I give them alfalfa.  All my others get the perinneal peanut hay. 

I feed perennial peanut hay and I supplement this with Timothy also (lower in calories) so he has more to munch on. What do you mean by can't tolerate it? Too much energy? Colicky? It all depends on what you mean by your statement.