If your talking about just using vouchers you can use them on your real account. It's completely safe, probably the safest way to get cheap food without fraud. Codes are 1 time use but you can use different codeson the same account. If your talking about the voucher method you can do the method unlimited times, and to do it you dont need to create grubhub accounts.
Hope I answered all your questions dont be afraid to ask more, have a good one. This is a bump