Yes, additional participants can be added to a Collaboration.

Organization users can be added as additional participants to a collaboration conversation at any point. The newly added members will then be able to see the entire conversation and documents attached to the respective Collaboration.

When a user takes action to invite someone from his company into a conversation, a list of suggested participants is displayed in the panel to help easily target the most relevant people to this conversation. The suggestions are calculated based on the document type, who else in the company collaborates with the supplier, who the user has historically added to collaborations, etc. The user can still perform the manual search & invite functionality to invite any specific user outside of the suggested group.