Sure, they can be integrated; I'm not sure how you got the impression they couldn't. What I meant was that the S1-S2 plugin has a specific purpose and is of pretty limited value, and doesn't really apply to your situation.
The Struts 1 plugin documentation describes how to use it--but again, I caution you that this really isn't what you're trying to do. Running S2 alongside S1 is fairly trivial--just set them both up, make sure the mappings don't conflict, and you're basically done.
Yeast devil! Back to the oven that baked you! And take this tiny ad too: