If you want them to help you with the idea or even join you some way to build it I wouldn't have any problems with showing them such document. The only prerequisite would be signing NDA but my guess is it's already signed.
Anyway, both vision and scope (in your case both in the same document) should be distributed as broadly as possible. In the old times some teams had this tradition of physically signing such documents to show their commitment. All stakeholders should know what exactly you plan to build and how much it is aligned with their goals. Clients should know it as well since they're basically buying the vision and the scope. Partners, and potential partners, should know what they're sign for (and this is you case).
If you want to discuss project with some outsiders you will eventually end up showing them the document so no need to show lack of trust from the beginning. If you fear that they would steal the idea first, we go back to lack of trust and rethinking whether you want to talk with those guys at all, second, that's what you sign NDA for, and third, this kind of scenarios are overrated -- most of companies care about their good name and don't want to be dubbed as thieves.
All in all, I wouldn't hesitate to show the vision and scope document to people who are considered as potential partners or anyone else who is involved in a project.