@Martyn Henderson -
Definitely! The article from @mlanders here (https://community.miro.com/got-a-question-ask-the-community-45/how-to-copy-content-from-a-free-acount-to-the-company-account-whiteboard-282) provides info on how to copy content between two different Miro accounts, but the principle is the same - once you have shared a board with a third-party account, they can take see it within a new Team and be able to access it.
However, as far as the licensing angle goes, that would be a good question to ask the Miro sales team as I don’t know whether such access would be still considered under your subscription limits or not.
Kiron
Thank you @Kiron Bondale, very helpful!
I have contacted the sales team so await their response
Martyn