Can a user use Gumlet as a service to transcode the clients' videos while keeping the hosting with their own architecture?

Yes, you can!
• Login to your Gumlet account.
• Click on the Video drop-down menu in the left panel and select Collection.
• Create a video collection using your desired source to import your client’s videos onto Gumlet dashboard, then transcode the video on Gumlet Video CMS and then serve the video on your own environment as per your need.
• For more Please refer to this link.