I need to know if free account holders will be able to collaborate on forms that have been shared

Hi;

This FAQ goes over Sharing - yes, a Free user added as a "Co-author" can collaborate, the permissions in the form itself are tied to the author, so if a paid author shares a form the form has paid level features for everyone shared with.  In addition the forms shared with Free users do not count against their form quota (of 1 form), they can have unlimited shared forms in their account.

Thanks,

Josh