(Nango co-founder here) We use the Elastic license precisely for the reason you mention: to prevent companies from rebranding Nango and selling it as it is. For all other use cases, it should be accessible.
My point is that if there is no clear boundary, it's too risky for me to try this product even if it's open-core. For Elastic, their boundary is "database as a service" but I don't see anything similar in your license.