Is the Ninja Form Zapier Extension supported?
Thank you for your question about Ninja Forms. If the extension you mentioned works with Ninja Forms, then you should be able to install it in your BoldGrid installation, since BoldGrid contains a fork of Ninja Forms.
However, it would be best advised as always to proceed with caution. If you have a development environment for testing, then I advise trying it there first. If everything works as expected, you can integrate this extension into your live site.