Each deal can can be linked to a contact person and organization. It can be done from the deal page at anytime, or when the deal is created. You are free to link any person and/or organization, no matter if they are linked to each other. You may link a contact person from another company.
Persons involved are not linked to the deal like the main contact person, but this feature will allow you to have a complete view of all the persons that are “participating”. People involved can be from any organization.