Thanks for sharing your reasoning but you're asking for far more than a logo on the homepage. Perhaps you could add a checkbox at signup that says something like, "Will you allow us to use your company name and/or logo on our homepage?"

That will give you a good idea of how your customers feel about this. It's probable that many people are signing up for your service and are not authorized to give you permission in the first place.

Good luck to you and your team. I'll think about sending in the email you mentioned.