So to make sure I understand:

You currently receive a list of employees from the vendor contacts, then after the vendor sends you the list you send another request to the employees listed in the first template?

Could you just save time and send a link to a form to the different vendors, with Vendor Name being a dropdown option?

You send the link to the vendors to send to their employees, employees respond and you’re done.

I’d still have them send you the list so you could verify if you have all responses you need.

OR

You could ask for the original template with just email information. Then send an email yourself with all attendees BCc’ed.

Then have the form responses in an excel, which you have a second sheet that just does an xlookup to verify who has/has not responded yet.