This isn’t legal advice, but check out the terms of service https://plot.ly/terms-of-service/.
User Content; License to User Content
You retain all rights to your User Content. User content means data, graphs, code, commentary, and derivative works you import, create, share, modify, and distribute through Plotly’s platform or products.
By setting your work to be viewed publicly, you agree to allow others to view, copy, and re-use your work and the underlying data. For any User Content that you upload to or generate through the Service and publicly share, you grant us a worldwide, perpetual, royalty-free, transferable, right to use, reproduce, modify, adapt, publish, prepare derivative works of, distribute, and publicly display that User Content. You may modify or remove your User Content via your Plotly account or by terminating your Plotly account.
Prohibited Uses: Community Subscription / Personal Subscription / Professional Subscription
Charts hosted on plot.ly, whether public or private, may not be embedded in any commercial, fee based application, service, or product. For information about OEM usage of Plotly, please contact email@example.com.
If this doesn’t clear it up, I’d suggest contacting firstname.lastname@example.org and clarifying whether your use case requires an OEM license.