Yes. The voucher will be sent to the email address that was provided in the sweepstakes or voucher entry form, not to whatever login address is used later.
For both the Microsoft Credentials AI Challenge and the Microsoft AI Agent Skills Sweepstakes, the entry form explicitly asks for the email address where the voucher code should be sent. Winners are then notified via email from “MindHub Pro by Pearson VUE” to that address, and the instructions emphasize using the same contact email when scheduling the exam so the voucher can be applied.
So if the Yahoo address was entered on the claim/entry form as the contact email, the voucher will be delivered to that Yahoo email, even if the Microsoft account sign-in email is later changed to a Gmail address.
References: