Can I integrate gumroad in my platform, in such a way that, my clients can simply put in their "Gumroad Key" and they can start charging their own users and collect payments?
After collecting payments, I would store in my database all the users who have access to client's content, and I would authenticate with gumroad, and then allow access to the buyers?
Stripe Connect may be better for you. The main issue I believe is actually taxes and reporting to IRS. Gumroad offers you a way to sell a product and sends you the necessary tax forms. If you're collecting on behalf of others then it complicates the taxes. Also do you have a way to manage the cash that you collect and send?
I had previously signed up for Stripe Connect and they had to ask me a bunch of questions about my business in order to approve me for the service. I'm not sure Gumroad is set up for this particular type of white labeling.