I don't see why not. As long as you keep the document well-formed (forms can't overlap each other),
you should be fine. I'm assuming that either you have each form have its own set of submit button(s) or if not, you are using JavaScript to submit forms. I prefer the former approach though.
As for displaying error messages, you have almost total control over how and where the messages will be displayed. Are you encountering any specific problems with using the tags?